Yves,
This is embarrassing... I made a mistake, running with some assumptions, and gave you some bad information. The assumption was that the parts on the existing tank were Brazed, not soft-soldered. Hussein's successful repair by brazing the joint, My chat with the folks at Harris, and the design of the joint itself all pointed me in that direction. But Jeff's comment about one coming apart unexpectedly tipped me off. I have an aftermarket Stainless tank on my car, so I examined it. Mine is definitely soft-soldered. I can slice into it with my pocketknife. It is probably an alloy similar to the "Stay Brite" (96%Sn/4%Ag) mentioned earlier. If yours is built the same way mine is, trying to Silver Braze it without first removing ALL the soft solder would have been a miserable failure.
For soft-solder to work well it needs much more surface area, like in the overlapping joint ngrandolph used to repair the outlet tube on his tank. I expect his repair will hold up, in spite of the comments from the tech at Harris.
I've got to give some thought to how best to approach the repair. Options include:
1. Just soft-solder it and give it a try. That's simple, easy, and cheap. It won't make anything worse, except for a small area of your chrome (which is unavoidable).
2. Re-design the joint, perhaps adding a piece with a ferrule & flange, to give adequate surface area to a soft-solder joint.
3. Take it apart, clean all the solder off, and reassemble it by brazing.
Again, I apologize for taking too much for granted in my assumptions. I believe that what I wrote about brazing in general is accurate, but it doesn't apply very well if the joint needing repair was soft-soldered to begin with.
Brian