The engine is a 25 HP Kohler Command off a Bob Cat ZTR. Should I replace the exhaust valve guide, or get a new engine? The engine has about 2500 hours on it. The lawn mower shop took it apart but they gave it back to me do to my money issues. I have a choice of having them put it back together with the new parts. Or I can put it back together with the new parts. Im a good back yard mechanic. Or I can buy a new engine. Whats a good choice?