Lee, I just completed a rebuild of my YSM12 over the winter. The cost was roughly $1500. in parts and some labour. The up side is being able to do the majority of the mechanical work yourself. I replaced or had rebuild everything under the sun(and I mean everything..... valves, piston, cylinder sleeve, fuel delivery system etc, etc, etc. I figured if the engine lasted 27 years it should do another bunch and there won't be that taunting thought at the back of my mind as to what will fail next....everything is new!!!