I'm not too familiar with pneumatic nailers. I bought one at a pawn shop recently to do the roof on a shed I just built and it stopped working on me. It seemed the piston wouldn't return to cycle and strike the next nail. I took it apart and the exhaust valve bumper (I think that's what it was) was like mushy wax. I pulled it out and put the gun back together and now it workes perfectly. I'm guessing bostitch didn't put it in there for no reason at all so what's happening inside the gun without that bumper in there?