Never in my life have I ever used a gasket for a muffler in 30 years. OS, Supertiger, ASP, ThunderTiger all metal to metal. If you need a gasket theres something wrong. Maybe an overheated engine at one time that warped the muffler, but I kinda doubt it. Have you tried another muffler? Also I have never had one come loose or fall off, never! Just bolt it on with Loctite on the screws. Thats it nice and simple.

Good Luck