Also, try the red high heat RTV stuff with your OS. I even had a regular muffler on my YS110 once and after a few flights(this is the included YS Muffler) it started vibrating lose and lost screws, etc. I have a pitts muffler on that engine and it works much better. I have had to re-tighten the OS after a few flights then it seems to go forever. I did break one of the exhaust manifolds on an OS 91FS on my stick after about 1.5 years of hard flying and I just bought another one and slapped it on, it did no damage to the engine at all.