You have a couple of choices...

I've tried JB Weld but it hasn't held for me.

What I ended up doing was putting RTV sealant along the rim.

Then putting the whole thing together, paying particular attention to screw that long bolt as tight as I could w/o stripping it, BEFORE putting on the nut.

Then I put loctite on the nut and put that on with a nut driver, and finally a second nut to act as tight as I can against that.

( this was suggested by someone at my field and it's worked GREAT ).

You could also drill a hole at the joint, then tap it for a small screw and put the screw in to prevent rotation and also to eliminate any potential loss of the rear part of the muffler.

BTW: Richen it just a tad. My T.H. engine will run with the muffler back off!

Just noisy as anything...

It may be sluggish, but it should not deadstick...

This happened to me with an inverted mount on an Ultimate ( glides like a brick! )... which I brought back after an additional trip around the airfield.