I bought a rebuilt-25K-ago 2F recently that had uneven compression, and 3 valves had zero (or negative) clearance. Ouch. After adjusting, the compression came back up (mostly), but don't wait to check your valves. This guy waited too long. At this point, I don't know whether to just run it and hope the valves re-seat, or to have the valves redone, again.
Colo Springs, CO