My vote is the car/truck only driven a mile or two, esp. in winter, and never fully warmed up. My late MIL had a Cavalier that she only drove back & forth to work, never got fully warmed up, it knocked the cam locating dowel off the camshaft several times (guessing due to poor lubrication). Add to that the sludge that seems to form when an engine is always used cold, that equals trouble.