I know this is locking the barn door after the horse is gone, but...
I always disasseble a new muffler as soon as I get it - put antisieze on the threads, replace any rivets with pem nuts, put in the correct amount of packing (sometimes there's not enough, normally there's too much).
Then we repack after every 500 miles or so of riding on the thumpers, after a weekend of riding on the two strokes.
I have purchased bikes with aluminum mufflers which have never been repacked. Bad news is, in most cases, the carbon is so welded to the aluminum that you can't get them apart.
Try the heat, try banging on it with a rubber mallet, stay patient -- but if it doesn't come apart after working on it for 1/2 hour or so -- leave it.
After a few years, the aluminum gets brittle and worn. Sometimes there's an actual lip inside the cannister where the steel baffle has worn into the aluminum. Basically it's welded itself together - no removing the baffle without destroying the cannister.
BTW, the 3" steel supertrapp does not require repacking.