Suspension: Koni strut servicing

Dr.Jeff

True Classic
I have a set of 4 Koni struts for the X1/9. They are new (as in never been used), but old (as in manufactured back in the 80's). Due to their extended shelf existence I decided the best thing would be to service them before installation. In this case I refer to a "service" as a complete tear down, inspection, cleaning, seal replacement, fluid replacement, and reassembly. This is opposed to a "rebuilding", which would include those items plus replacement of the bushing, any worn/damaged parts, and possibly revalving. I did not take photos until most of the work had been done but here is a brief summary (not intended to be a detailed "how to"). The photos I have (at the end) will help to follow the description, but a little back and forth may be needed to see things as we go along.

These Koni's were specifically made for the X1/9 application, to replace the stock struts. So they had standard spring perches and install using the stock mounts. Their dampening is 'adjustable', but only for rebound (compression is not adjustable). I'm not sure how their valving compares to the original stock Fiat struts, but imagine they were considered an upgrade and therefore firmer. Depending on the springs utilized, the dampening could be externally adjusted to suit. For my use I am converting them to coil-over units. Therefore I cut off the stock spring perches and added retaining rings to allow the addition of threaded collars. The springs that will be used are stiffer than the stock springs but not by a lot. I want a decent quality ride for normal street driving, but a little firmer for handling and to prevent bottoming out - they will have an adjustable ride height enable lowering the car (purely for aesthetics).

Disassembly begins by removing the top nut (collar or cap). These nuts have a pair of holes in the top of them and round circumference. Therefore you can't use a regular style wrench, but must use a special removal tool. These tools are available but not worth the cost for my needs, so I made one. I also made a simple wood fixture to hold the housing in a large vice while working on it.
After that nut is removed, the seal / rod-bushing assembly is pulled out. This does not come out easily; there is a O-ring to seal it into the outer tube (housing), and some sort of force is needed to slide it upward. I fashioned another tool to do that, utilizing a slide hammer and adapter piece. For reassembly, the seal/rod-bushing assembly must be pressed back into the housing. I used a couple of left over urethane bushings to do that.
Next the main shaft (rod) can be drawn out, along with the inner tube assembly. The bottom end of the inner tube holds a valve disc assembly. Connected to the end of the main rod there is another valve assembly. One valve controls compression movement, the other rebound movement. There is a stack of thin discs in these valves. By replacing the discs you can revalve (tune) the dampening action as desired for compression and for rebound. For my needs I wanted a slightly firmer overall dampening effect but did not want to completely revalve it. So I replaced the fluid with a heavier weight suspension fluid instead.

Although these units had never been used the insides were rather dirty. The original fluid in them was petroleum based and degrades over time, even without use. Plus a minute amount of moisture in the air trapped inside them contributes to further decay. To thoroughly clean them, everything needs to be completely disassembled (including the valve assemblies, etc). Keep track of all the little bits and be sure to replace them the same way they came out. I used synthetic suspension fluid of approximately 40% heavier viscosity. But that does not equate to a 40% stiffer action (it has less of an effect than the numbers might suggest). New Viton seals and reassembly in the opposite order.

Here are some pics. They were taken during assembly, but I will show them in reverse order to represent disassembly:

1) The complete strut assembly, with modified outer housing and coil-over threaded sleeve.
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2) The outer tube/housing and the inner tube dampener assembly.
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3) Top nut/cap. Notice pair of small holes through it (not well shown here). The removal tool has a pair of pins that attach into these holes.
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4) Main rod/shaft and inner dampener tube. The rod slides through the seal/bushing assembly. There are two disc valves; one is on the inner tube, and the other on the rod.
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5) Close up of the two valve assemblies. These are what can "tune" the shock ('revalving') by changing the discs inside them.
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6) Close up of the main rod seal and bushing assembly. There are two seals; a O-ring to seal the assembly to the outer housing, and a lip seal to seal the main rod as it travels up and down. The lip seal is what wears and allows fluid to leak outside of the strut. A sleeve bushing inside this assembly is what the rod rides on. When it wears the rod gets side-to-side play, allowing other things to wear out quickly.
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7) Some simple tools I made to work on the Koni's.
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Later I might take a photo of the completed coil-over strut assembly ready to be installed. I can also give a few more servicing details and photos if requested.
 
Someone asked me about the valves that can be tuned. Here is a little more detail, but again no pics of everything completely apart (sorry).

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Both sides of the valve on the end of the dampener (inner) tube:
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The two valves are very similar. Each has either a screw or bolt in the center that holds all the parts together. Removing that fastener allows the discs and other pieces inside to come apart. Basically as the fluid is forced past the discs/orifices, the small passages restrict the rate of that flow. The number and specific design of those discs (and other parts) changes the flow rate and therefore the dampening characteristics. One has a coil spring, the other a wave spring inside. The springs make them a 'one-way' valve; fluid can pass fairly freely in the opposite direction. That is how one valve controls compression and the other rebound. Even changing those springs, as well as the retaining end plates, can alter its function. By having two separate valves, one for compression and one for rebound, the two functions can be tuned independently.

As you can see, one valve is attached to the end of the main rod (the piston), and the other to the end of the inner tube. The outer strut housing acts as a reservoir for the fluid. And the inner dampener tube is where the piston (end of the main rod) travels inside. The inner tube and piston are a calibrated fit (wall clearance), so the fluid must pass through the valves as the piston travels.

Looking at the first and third pictures above. The two tangs on the piston valve (first pic), either side of the retaining bolt, can engage with the two recesses on the back side of the dampener tube valve (third pic). When the main rod is completely compressed, those tangs and recesses interlock. Turning (rotating) the main rod from the top (externally) turns that rear portion of the dampener-tube valve. That changes the flow rate past the valve. This is how the unit can be "adjusted" externally for rebound. There is approximately 1 3/4 turn of movement possible, proportionally changing the flow. One potential problem with the unit's design is the valve on the end of the dampener tube is a press fit onto that tube. For some reason it is not a tight press fit; most of mine just fell off the tube when disassembling things. Therefore when the rod is compressed and rotated the entire valve can spin inside the tube, preventing any accurate adjustment being possible (the whole valve rotates instead of just half of it). During reassembly I peened the end of the dampener tube to help better secure the valve in place.

For a thorough cleaning it is best to disassemble the valves and clean the individual parts. Being small orifices, that is where debris will tend to collect, much like cleaning the inside aspects of a carb. Especially being located at the bottom of the entire strut assembly where stuff gathers. And those orifices are what control fluid movement (dampening).

These valves are the heart of the shock/strut, they define its characteristics. Koni offers a selection of replacement parts to help tune it, but knowing what specific ones are needed would require a shock dyno. And as mentioned, every part of the valve plays a role in its performance. So to properly do a revalving you probably need to send the unit out to be done. Likewise if the bushing is worn it is difficult to replace without the right equipment. But the shock unit would need to be very used for that much wear of the bushing to happen. The main rod itself can also wear. In some cases it can be rechromed to bring it back to specs. But to get it to the right finish and size might be difficult, otherwise it will allow the lip seal to leak. For these reasons doing a 'service' rather than 'rebuild' yourself is more practical. Just cleaning, replacing the seals, and changing the fluid makes a big difference.
 
Thanks for posting this. Great info! Where did you source replacement seals - direct from Koni, aftermarket or hydraulic shop?

Having recently done a full service on a modern mountain bike fork, the Fiat Konis look pretty simple!
 
Where did you source replacement seals - direct from Koni, aftermarket or hydraulic shop?
I've also done mountain bike forks before and they are kind of similar. Really all dampeners are.

Getting the right seals for Konis sort of depends....
The O-rings are nothing special. I opted for Viton only because I feel like they are a bit more durable, but it isn't necessary. Suspension fluid is hydraulic fluid with a couple additives, so it is compatible with pretty much all seal materials.
The top main seals are basically "lip seals" (often referred to as 'shaft seals'). However the exact design differs on various Koni units. Even the sizes can be odd (non standard). Mine happened to be a match for some rather generic (although not extremely common size) hydraulic lip seals. But not all Konis are. You won't know for sure until the seal is removed and identified. And the way that Koni mounts them, you will destroy what's left of the seal getting it out. So a bit of a crap shoot. However Koni does offer most of their old seals, but at a price. I have a hydraulic seal supply house that gets me just about anything I need and they found some that worked at a very good price (a fraction of what Koni wants).

I didn't mention it but Konis can have a lot of deviations from model to model. For one thing there are units that have external adjustment for both compression and rebound, which are very different inside. And there are other levels of performance such as Koni 'red', 'orange', 'yellow', etc. A long time ago I went through some Koni shocks (not struts) for another vehicle and they only had one valve assembly inside (instead of two) that served both compression and rebound functions. In the case of the ones that I have for the X1/9, the front and rear units are different. The ones I showed earlier have a slightly different arrangement for the top nut, seal/bushing assembly, and lower piston than the other pair (front vs rear). They function the same and the general servicing process is the same, but the details differ. Plus their designs evolved slightly over the production period. Which is why the exact seals may be different from one to the next. And that's why I decided not to do a step by step 'how to' tutorial.

But I can offer a couple other general guides. The fluid inside comes in a selection of viscosities, roughly from as little as "1 weight" to as much as "40 weight" (and I'm sure there are more). According to the Koni engineer I know, they use their own proprietary blend of fluid (pretty much every dampener maker does). But it really isn't that critical to use their blend. However the viscosity you choose will make a difference on how the unit performs. He said these can use as light as 10 wt to as heavy as 30 wt. The original fluid for mine (remember it can vary from one to the next) was 20 wt, but I went with 30 wt for the stiffer springs I'm using. Another factor is the quantity (volume) of fluid. This actually makes a bigger difference than the viscosity. There needs to be some air space inside these sealed units, the balance of air and fluid changes the dynamics. He told me my fronts should have 240 mL and the rears 230 mL of fluid each, which is interesting because the rears are longer and can hold more fluid. I chose a synthetic fluid but it is available in different blends. The most affordable fluid source is motorcycle supply stores. They carry a wide selection at a great price. Or again you can get the actual Koni stuff for a lot more money.
 
NOTICE to CARL: this content refers to the damaged Koni strut from your recently wrecked car. You may not want to view this post if it is too soon and the wounds are still healing. Sorry.


As most of you already know, Carl recently experienced a very unfortunate event where an idiot driver totalled two of his X1/9s. On one car the damage seemed to focus on the rear wheel/suspension area.

IMG_0729[1].JPG


This caused significant damage to the Koni strut that was on the car. I asked Carl if I could play with the old strut to assess the damage to it. He sent it to me and today I tore it apart. This also gives an opportunity to add a couple photos that I omitted in my earlier posts (above) on rebuilding Koni struts.

Here is what the strut looked like after the accident:
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The first step in disassembling (or rebuilding) a Koni strut is to remove the top nut. These are typically very stubborn, so a lot of clamping force and leverage is required. To secure the strut in a large vice, I use a simple wood jig made from a piece of 2X4:
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The top nut has two holes in it. A "special Koni tool" is required to remove the nut by inserting it into the two holes. I don't have that tool so I made one from a old 'Crescent wrench' and a couple pieces of round stock:
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Tool in position:
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Top nut removed. In this case the nut and the seal/bushing assembly came out together. They are actually rusted together. Normally these should be two pieces, as seen in my earlier photos (see posts above):
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Here is the top portion seen up close:
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I've reached the 10 pic limit, so continued in next post....
 
Looking at the upper seal and bushing assembly, we can see the bushing (where the main shaft rides):
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And the seal on the other end (upper most portion of the strut tube), where the main shaft is sealed:
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Old suspension fluid looks very nasty:
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You can see that the inner metal sleeve that the main shaft and piston travel in was damaged. It isn't obvious here, but the tube was bent (long axis) as well as dented (seen here):
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This illustrates how the shaft and tube are bent relative to one another. Notice the difference in the gap on either side:
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As it so happens, this strut was on its last leg anyway. The main shaft has scoring (see pic), allowing the top seal to leak, therefore the fluid was contaminated with water due to the leaking seal, which resulted in rust on some inner components. So it would not have lasted long. The seals and fluid could have been replaced to extend its life a little, but the other issues would eventually kill it:
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Just because I like to cut sh*t up, here are some views of the damaged outer housing:
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Greetings Jeff,

I decided to service my rear Konis, since the car will soon see some competitive use. Last night I opened the first one and drained the fluid, you can see it on the left in this pic, with fresh fluid on the right.

koni oil.jpg


These shocks have never leaked a drop and interestingly there was only 150ml of fluid. Quite different to yours, but mine are inserts, so understandable. These shocks are part # 82P-1894. My fronts are 82P-1893. I might also service them, but they don't really need it yet. If I do, I will record the volumes!

Anyway, I'm a little embarrassed to post the pic above, since it shows my shocks were overdue for a service!

Thanks for your great write up of how this done.

Cheers,

Rob
 
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Greetings Jeff,

I decided to service my rear Konis, since the car will soon see some competitive use. Last night I opened the first one and drained the fluid, you can see it on the left in this pic, with fresh fluid on the right.

View attachment 62958

These shocks have never leaked a drop and interestingly there was only 150ml of fluid. Quite different to yours, but mine are inserts, so understandable. These shocks are part # 82P-1894. My fronts are 82P-1893. I might also service them, but they don't really need it yet. If I do, I will record the volumes!

Anyway, I'm a little embarrassed to post the pic above, since it shows my shocks were overdue for a service!

Thanks for your great write up of how this done.

Cheers,

Rob
Rob, great to hear from you. That used fluid is very typical looking. Even after normal use it gets like that within a relatively short time. As you said, insert cartridges have a smaller internal volume (narrower tube) and will use less fluid. Also fronts and rears are different lengths so they have different volumes. Finding the correct amount to fill one that has been leaking can be a challenge because you'll not know how much leaked if you measure what's left. The capacity spec should be found online for more common models, but the ones for a X aren't very common. Luckily you won't have that problem since yours did not leak. Therefore you can put the same amount back in. By the way, the actual amount of fluid that goes inside can vary the shock's behavior. Therefore in some cases it may be favorable to slightly over or underfill them. But you can also change the viscosity of the fluid to achieve similar results. Speaking of viscosity, Koni changed the fluid weight considerably over the years. It started fairly thick in the early days but they used lighter and lighter weights over time. I assume the valving was also changed to accommodate that. Also, since yours weren't leaking I'd leave the main seal alone. Koni is one of the companies that likes to use proprietary designs of main seals and the replacements for most older models like these are no longer available. So don't damage those seals as you work on them. The O-ring is standard and can be found generic. Mine had swollen considerably to the point they would not go back in, so I had to replace them.
 
@Dr.Jeff I missed this thread when it came out, I am glad someone dredged it back up. My Koni’s hopefully can be serviced, they came off a low mileage early X in California and then banged around in boxes for decades so I am sure the fluid at the very least needs replacement. Nice tool development
 
@Dr.Jeff I missed this thread when it came out, I am glad someone dredged it back up. My Koni’s hopefully can be serviced, they came off a low mileage early X in California and then banged around in boxes for decades so I am sure the fluid at the very least needs replacement. Nice tool development
Karl, glad you enjoyed the writeup. It isn't uncommon for the struts to develop leaks just from sitting, as the main seal rubber hardens/shrinks over time. But that usually results in them seeping oil and the bottom of the box will be soaked. If yours haven't leaked after decades sitting on the shelf then the main seals should still be good. As I mentioned previously the correct seals are no longer available so best to leave them alone. However the struts can still be disassembled, cleaned, and the fluid replaced without harming that seal. The top O-ring is easy to source.
 
I have paid Truechoice Koni Racing Services to modify and refurbish the Koni struts I use on street X's and my racecar. The last time I had struts refreshed was 7/6/21. I don't think they are in business anymore, at least the website is down and the phone doesn't work. Maybe the folks at MWB would know, they are local to them?

Anyway...when the refurbished my struts they used new seals and o rings. Part # 1601 70 00 08 tube seal, 1601 70 01 27 o ring. They also sold me shock oil - by the gallon. Don't know if those numbers help or not?

I don't know if you can get the parts, or oil anymore, but I do believe that there are others that will rebuild your struts. Both Koni (a long time ago) and Truechoice modified my struts for me (Truechoice had access to the build data for my struts from Koni). They cut off the spring perches for coilovers, shortened the body and rod (very important if you want to lower the car substantially), custom valved them to my app./spring rate range, made them externally adjustable for rebound, and dynoed them.
 
Several years ago Koni moved all of their authorized services to one company in Calif. And that company will not sell any parts. Making it necessarily to pay their inflated prices for them to do any work themselves. That's why the seals are no longer available.
 
Truechoice is no longer in business and there appears to be only one rebuilder left in the states (located at Sonoma Raceway). I was SHOCKED to see what they charged me for rebuilding my Koni 8211 shocked for my Formula Ford. They have an $450 EACH for a job that Truechoice used to charge $250 for.

If you send them out, make sure you get a quote first..
 
only one rebuilder left in the states (located at Sonoma Raceway)
That's the one I was alluding to earlier. And yes, they are outrageously expensive. Unfortunately they are the only facility that Koni authorizes to do any work on their products, and therefore the only source for all parts. And as I stated earlier they will not sell parts separately. Since Koni does not offer direct service themselves so there's no other options for authentic "Koni" parts (like the proprietary seals). As a result even if one of those seals was still in production you could not buy it.
 
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Rob, great to hear from you. That used fluid is very typical looking. Even after normal use it gets like that within a relatively short time. As you said, insert cartridges have a smaller internal volume (narrower tube) and will use less fluid. Also fronts and rears are different lengths so they have different volumes. Finding the correct amount to fill one that has been leaking can be a challenge because you'll not know how much leaked if you measure what's left. The capacity spec should be found online for more common models, but the ones for a X aren't very common. Luckily you won't have that problem since yours did not leak. Therefore you can put the same amount back in. By the way, the actual amount of fluid that goes inside can vary the shock's behavior. Therefore in some cases it may be favorable to slightly over or underfill them. But you can also change the viscosity of the fluid to achieve similar results. Speaking of viscosity, Koni changed the fluid weight considerably over the years. It started fairly thick in the early days but they used lighter and lighter weights over time. I assume the valving was also changed to accommodate that. Also, since yours weren't leaking I'd leave the main seal alone. Koni is one of the companies that likes to use proprietary designs of main seals and the replacements for most older models like these are no longer available. So don't damage those seals as you work on them. The O-ring is standard and can be found generic. Mine had swollen considerably to the point they would not go back in, so I had to replace them.

Well, after 1 rally I found my front konis are leaking. The seals are shot although they weren't leaking while sitting on the shelf.

These are the two seals I need to replace:


IMG_7281.jpg

This one is easy, 38mmO.D. and 3mm thick, I have found appropriate o-rings on McMaster-Carr.

IMG_7284.jpg

IMG_7285.jpg

It fits between these two parts and seals against the outer insert tube.

IMG_7282.jpg

This one will be a bit harder.
O.D. of what I'll call the base is 30.5mm
Total thickness is 8.2mm
Base thickness is 2.5mm
The upper section is slightly tapered
I.D. at the top is 19.75mm
Shock shaft diameter is also 19.75mm

It fits in this grove in the top cap and seals against the shaft

IMG_7283.jpg


If anyone has any ideas on where I can find a suitable replacement, please let me know.

Cheers,

Rob
 
If the leak is from the center main shaft then that second seal you showed is the one that needs replacement. And it's the one I was referring to when I said they may not be available anymore. Unfortunately most Konis used a proprietary design that doesn't match any universal seal. And they no longer sell parts to customers. The only route that I'm aware of is to send the units to their sole authorized service facility where they will charge you a fortune to completely rebuild them. Perhaps you can get lucky and find some left over from one of the other facilities that are not authorized Koni repair shops? Although I think Koni has pretty much forced them out of doing a lot of work by not supplying them such parts.
 
If the leak is from the center main shaft then that second seal you showed is the one that needs replacement. And it's the one I was referring to when I said they may not be available anymore. Unfortunately most Konis used a proprietary design that doesn't match any universal seal. And they no longer sell parts to customers. The only route that I'm aware of is to send the units to their sole authorized service facility where they will charge you a fortune to completely rebuild them. Perhaps you can get lucky and find some left over from one of the other facilities that are not authorized Koni repair shops? Although I think Koni has pretty much forced them out of doing a lot of work by not supplying them such parts.
Hi Jeff,
I contacted the local authorised Koni service guy and he said he doesn't sell parts, but he can rebuild my shocks for me. But couldn't/wouldn't give a quote. Basically send them, he'll fix them, then tell me how much it costs.

Like you I've easily found a source for viton o-rings at a very reasonable price, just $5.72 each. Bot hexisting o-rings are hard and deformed and can see that they aren't sealing. I've not found a replacement for the rod wiper seals I showed earlier, but have been told that soaking them for a few days in silicon lubricant will rejuvenate them, so I'm trying that. Apparently it replaces some of the rubber softening agents that are lost over time. We'll see if it works.

I have discovered that there is a seal pack inside the gland nut at the top of the insert.

IMG_7283.jpg


I made a tool to remove this top ring, which wasn't very tight. Underneath there is a solid washer and the two spring washers. Then there is a brass coloured washer (which you can see) which I haven't removed yet. It is a tight fit and I'm soaking it with penetrating fluid. According to this write up on this site:


there is a seal pack under there. I'd like to get them out and clean them and wonder if getting the right tension on re-assembly will result in a good seal again. If I can get them out I'll see if I can source replacements.

Our Konis are becoming rarer and definitely worth saving.

Cheers,

Rob
 
Our Konis are becoming rarer and definitely worth saving.
Agreed.

I contacted the local authorised Koni service guy and he said he doesn't sell parts, but he can rebuild my shocks for me. But couldn't/wouldn't give a quote. Basically send them, he'll fix them, then tell me how much it costs.
That's pretty much how the sole Koni authorized service facility in the US operates also. Sucks.

I've not found a replacement for the rod wiper seals I showed earlier, but have been told that soaking them for a few days in silicon lubricant will rejuvenate them, so I'm trying that. Apparently it replaces some of the rubber softening agents that are lost over time. We'll see if it works.
My personal take on the "soaking" process is it will not do any good. From a scientific perspective it is impossible to replace the chemicals that have been lost from the rubber. Unfortunately there isn't any process that can move molecules into the compound after it has been formed and cured. So the results won't be as hoped. However I'd absolutely love to be proved wrong on this, as would the scientific community in general.

I have discovered that there is a seal pack inside the gland nut at the top of the insert.
Looking at your pictures I see your struts are a different design than any I've dealt with for the X. The top gland area on yours looks different from mine. Are yours a universal Koni model (e.g. some of the ones used for race cars or such) adapted to fit the X? It's possible Koni offered a different design at some point, although I've worked on some very early and late ones and they were all the same basic design. Anyway, mine do not have another seal inside the upper portion like you described....just the O-ring and the wiper lip seal for the main rod. If I'm understanding you correctly, yours have a third seal?
 
I'm not sure on the soaking process either, and as a scientist I wonder if it is black magic. But we'll see.

The top of my struts are different to yours. I have another front insert that looks more like yours.

Based on the link I included for the Lotus shock rebuild, which looks like the top of my insert, there is what is described as a seal pack. It may not be seals, I'm not sure, so keen to get it pulled apart. This is what came out of the Lotus insert:

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That rubber part is what I am currently soaking.

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Then there was all of this in the Lotus example. So far I have removed the top five elements. I'll be curious to see how many more parts there are and what they are. Stay tuned...!
 
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