I have been using high temperature RTV for the last 4 years and I haven't had a muffler come loose since. You can purchase this at any auto supply store. I used to use the red but last year I changed to the black that GM uses for exhaust gaskets. Don't use a gasket between the engine or muffler or the muffler will become loose as soon as the gasket is blown. Use the RTV on the threads and all mating surfaces. Your muffler screws will remain tight and you won't need a torch to remove your muffler if you try this method.