It seals fine at the head of the engine, but it leaks out the front screw and where the two halves meet. I'll give the silicone a shot, and see if my other muffler fits. I think it has the same flange pattern, just not sure if a bigger muffler will be good for the power curve. I want it sealed because I am putting an exhaust tube on it to keep the oil from getting all over everything. It ran well with the test tube on it already.