Knight.. : Make sure that the mating surfaces are flat and square then see if they match up correctly when mated. The gasket is not necessary. Tighten the mounting bolts as tight as you can get them, use nylocks if you can fit them in there. Put the stronger (I think that's blue) locktite on the CLEAN threads where the nuts are going. That should hold it in place.

I have a Super Tigre 75 that had muffler problems. The inside of the muffler (the baffle) came loose. They sent me a new muffler and after a few flights it too had the baffles come loose. I opted to a tuned muffler (note the word muffler because they have pipes without baffles and mufflers with) and header. This not only increased the power but I no longer have a plane that sounds like jingle bells when it passes overhead.

DS.