I've done some battle with keeping my tower hobbies mufflers together in the last few months.. I have the one for the .75 and I think that I have finally convinced it to stay on.. Went to Ace Hardware and bought a piece of threaded rod as close to the through bolt that came with the muffler.. (It will be a little bit bigger). Get two of these guys because you will destroy one of them getting this set up.. Take entire muffler apart, so that you have three pieces. Take one of your threaded rods, and thread it into the front section of the muffler. The metal is very soft, and the bolt itself will make new threads perfectly. Once you get it through, thread it back out and put your other threaded rod into the threads you just made, with about 1/2 inch coming through the front part of the muffler. Put a drop or two of RED locktite on the portion of threads sticking out of the front of the muffler and use 2 jam nuts to hold the threaded rod in place. Let this sit overnight. I needed two rods because the pliars that I used to hold the first rod steady while threading the muffler tore up the threads pretty good..)

Now, use High Temp RTV Silicone and attatch the center tube to the front muffler section. For the aft end of the muffler... Get a drill bit that is SLIGHTLY larger in diameter than your through bolt, and drill our the threads in the aft section of the muffler where the old bolt would come through. After you have that squared away, use more RTV on the center/aft joint and put the aft end on the muffler. You will have more threaded rod coming through the aft end, cut it off later.. Now use red loctite again, and double jam nut the aft end in place. I think with the threaded rod you can put it on a bit tighter without worrying about it breaking..

Lastly, get a few very small sheet metal screws and pin the front/middle/aft sections together with the screws...

So far no leaks, no turning on the back end, and most importantly its still on my plane!!@