jrhelm,

First of all, get rid of the gasket. The gasket allows the muffler screws to loosen due to vibration. Use RTV in place of the gasket. It doesn't take much to seat the metal-to-metal surfaces. The clear 732 type is fine, but if you want to spend a little more, the high heat types will also work. Personally, I just use the clear.

Second, use locktite (red or blue) on the screw threads making sure they are as clean as you can get them. I generally use acetone for this. Let it set over night and you sould be good-to-go.