RE: DLE 55 Exhaust
This topic has been heatedly discussed before, so I will just pass something on that worked for me. Try using red high temp silicone on the bolts. Permatex is one brand that sells it and you can pick up a tube at your local auto parts store.
Also, make sure the flange of the muffler and the cylinder head are not scored or gouged from your previous mufflers coming loose. If so, clean it up the best you can.