i have never seen an oring on any mufflers for the 2 strokes,if it has been leaking you can use the rtv that wont hurt at all between the joints.i would use a nylon tiewrap around the muffler make it as tight as you can if the screw comes loose at least you wont lose half of your muffler i started to do this on all my mufflers wrap it around the exhaust and where it bolts to the engine.and like RCKEN said tighten the screw and nut use some fingernail polish on the nut providing it uses one most i have seen do.hope this helps some....