There's also the problem with the difference in the coefficient of expasion between aluminum and steel. The muffler will get tight and stretch the screw when hot and then be loose when cold?

I lost some too. GMS has had about three different designs of the screw because of this problem but none of those has solved the problem.

The first one I had was of the 2nd design. I lost the back end like you did.

I put a piece of threaded rod, I'm thinking 4mm, but 4-40 should work, all the way through the muffler with double nuts jammed on both ends. I never had anymore trouble. Self locking nuts do not work because of the heat. A single nit will not stay tight against just the aluminum. I never had anymore trouble with the muffler and that was years ago.

The second version did not have a head on the screw. The front piece was threaded and the screw would pull the threads out of the front piece.

Enjoy,

Jim