Hi Brad. Well struts are really just a shock with a spring perch welded onto them. Yeah, lots of cars use them. And yup, the X1/9 has them front and rear. And like any shock, they can get bent or rusted or leak.
You ask: "can they be rebuilt ? Should they be ?
Answer: well sort-of yes. I think your X is '77 ish ? Well up to about '78 or so, X1/9s came from the factory with "rebuild-able" struts that could have the shock portion of them rebuilt. There is a funky nut where the shock portion enters the strut casing. If... you undo that nut (actually requires a special tool that you would have to buy or make - but usually you can undo it by tapping the nut around with a drift ) all the innards of the shock will yank out of the housing. In theory, you could replace any worn/broken bits, and replace any leaking seals, fill it with fresh shock fluid, re-assemble, and voila you have a re-built strut. Well in theory that is....
In reality however - it is not so easy. Trust me on this one - if the valves are gummed-up/mangled or worn, or if the strut housing is bent, or if the chrome rod is not perfect (not bent, absolutely no pits/gouges/scratches/rust/wear ), this exercise is pointless. Best case scenario is that you only need new shock oil (easy to obtain) and a new seal kit. But new seal kits have been NLA for many years now. Although if you look hard enough you can probably find them. I think Obert might still have some. And once in a while they show up on Ebay Italy. But even then watch out - I think Fiat had more than one supplier for the original struts ( names like Wayasso and Riv ) and it is possible that the seal kits for each are different ?
Because of all the above hassles, and the high labour rates involved, way back then the common solution was to just remove all the innards and discard them. And replace with a sealed cartridge unit (also known as a strut insert). That just slipped into the strut housing and was secured by that big funky nut. Easy. It replaced all the moving parts - and the shock shaft of course. Back in the day they were readily available from many shock suppliers - Gabriel, Munroe, Sachs, Boge, KYB, etc. Even Koni with some nifty adjustable ones. By the way Bilstein never made an insert for the X1/9. But alas, pretty hard to find these days. Most suppliers seemed to discontinue them many years ago. Once in while they will show up on Ebay. The only ones I have seen on a semi-regular basis are the KYB. I think they made both oil and gas charged units. For sure KYB USA discontinued them many years ago here in North America. You can still seem to get them in Europe. Not sure if they are current production or just some NOS units still floating around. But even if you do find them, they will usually be pretty expensive once shipping is factored in...
You can now see why I said "well sort-of yes" LOL. For more discussion on this subject, see this recent post:
https://xwebforums.com/forum/index.php?threads/front-shock-questions.31754/
By the way, starting in around '79, all X1/9s came from the factory with "sealed" struts. That is, the shock innards were sealed into the shock housing, and the strut could not be re-built, and a strut insert could not be used to fix a leaking shock. To fix, you had to buy the whole strut ( just the housing and shock bits, not the spring and upper mounts of course). More expensive of course. Back then replacements were available from Fiat themselves of course, and a bunch of aftermarket suppliers like KYB, Sachs, Boge, Koni adjustable, etc. By the way never from Bilstein. Of all these, only KYBs seem to still be available here in North America (only in a gas charged version, I think the oil version is still available in Europe). But at least they are dirt cheap and easy to get - just poke around Ebay or any of our Fiat vendors. Some folks here love them - some dont like them. Other than that, not much around these days. Once in a while, other struts pop up here or on Ebay. Even NOS genuine Fiat units. I think maybe Obert or MWB have them sometimes too.
In the front of your '77, you CAN use the later '79 on sealed-type struts in place of your re-buildable types. But in the rears, the later '79 on struts are a bit different. You CAN use them in an earlier X1/9, but you must then use the later type upper spring perch.
That should about cover the stock-type replacement shocks. And yes, some should offer improved performance. Choose wisely !! And one note of caution here - be very wary of ordering any rear struts from Europe. It seems...some of the euro spec rear struts had a much higher spring perch than the NA spec. Not sure if those cars had a shorter spring to compensate or exactly what the deal is there. But some folks here have installed them and found their rear end jacked up an inch or two. Not I think what you want.....
Of course, you can always change to coilovers - but that is another whole discussion......
Hope this helps. And by the way Brad, you really want some CD27s ?? I still have a set....
Cheers, Doug