The JB weld wasn't the fix. The drill, tap, and threading in of a stainless bolt was the fix. The JB weld was just to keep the bolt from backing out, like loc-tite, and I just smeared the leftover around the bolt on the inside of the muffler just to use it up and keep water from settling directly onto the aluminum again.
I checked it out 2 years later, and all looks as good as the day I put it all in. 100% salt water use (my XP)