RE: Securing the Muffler
Try a couple of wraps of teflon pipe thread tape on the bolt threads. Tighten the bolts down as usual, and as mentioned above re- tighten after the engine and muffler are hot. I've found that loctite seems to allow things to vibrate loose and then seems to wear the threads out even faster. The teflon tape seems to work the best for me. Also don't use a gasket.
bhady