I am surprised how difficult some of you have made this problem. I have been flying R/C since 1972. In those days the mufflers, if used, were a piece of garbage compared to the wonderful mufflers our hobby uses today. Most mufflers in those days were actually strapped to the engine cylinder with a worm-gear clamp. Here is what I have been doing for about 20 years or so. Clean everything on the muffler down to clean metal, including the flange surface to the engine. Use Permatex Silicone Automotive Adhesive Sealant (I purchase mine at AutoZone)on ALL flange surfacesthe flange between the engine and the muffler; the surface between the two halfs of the muffler. Use Blue Loctite on ALL of the threads; the two muffler mounting bolts; the tapped thread in the muffler that the long central bolts thread into; the center bolt nut. I also add the silicone sealant under the head of the center bolt. Everything will be tight and leak proof for at least 6 months of flying. At the first sign of any leaking, or anything getting lose, take everything apart and do the whole thing over again. I assure you that it takes a lot more time to write this than it does to follow these instructions and end up with a job you can be proud of.