FYI only the type certificate holder can issue a new data plate, and they never do unless it is lost and you have a letter from the FAA. So if someone has affixed a new data plate that doesn't match the airworthiness certificate or registration, I would investigate that before buying it. A dead cylinder that comes alive after 10 min run is probably the result of a stuck valve. In any event that cylinder should come off for inspection/repair/overhaul before flight. If someone annuals this aircraft in the condition you're describing, I'd be very suspect.
-Joel Marketello A&P, IA