Just got a J15 RCOB commercial given to me, completely disassembled in a box. (Oh Boy!) engine swallowed a screw and bottom piston is a little dinged up but the rings are free. no scoring on the cylinder walls. I'm thinking about cleaning up the piston, honing the walls & giving it a try. I've heard that these models are almost bulletproof if the cyl.walls are good. Should I replace anything else other than new head gasket? Thanks!