that is common with most os engines. i would HIGHLY reccomend that you buy a piece of 4-40 threaded rod, run it all the way through the muffler, and secure it by locking nuts (nylock) on either side. sure it does not look quite as good, but you will never strip the phillips head out ad one end (which also happens a lot) and you will never have to worry about loosing that nut again. i lost the balk half of my muffler once, becasue i did notdo that, and i replaced it with the setup i mentioned and it looks fine, and works fine.