Sealing muffler to engine...this works for me!

[blue_collar2]

I've started taking very thick aluminum foil and cutting a "gasket" to fit between the two. Tighten the assembly up, and I haven't had any leaks. No sealant, no epoxy.

Anyone else try this?

[BarracudaHockey]

If the surfaces are flat you dont need anything.

What can happen is the different expansion rates of differing materials cause the muffler to loosen in flight. But if it works for you thats hard to argue with.