A group of guys I fly with, have been using the KS Aluminum Muffler gaskets available from Horizon.
http://www.horizonhobby.com/Search/D...Id=EPMA&Page=4
I had been using the Hi Temp silicone for many years with great results, but it is nice to be able to swap engines at the field, and not have to clean and wait for the silicone to dry.
Randy