I had the same problem years ago with an O S 1.20 FS. Nothing seemed to fix the problem. I finally J B welded all the fittings and never had another problem. But if you use J B Weld, you aren't ever going to be able to take the exhaust system apart. To use the J B Weld, you will have to clean all fittings extremely well. Might have to take them to a machine shop to get all the gunk off, or use a Dremel wire wheel. It's got to be very clean or the weld epoxy will not stick.

pmw