IamSam

Hello all! I'm looking at buying an xj900, but I have a question that's been stumping me. Mechanically the bike seems sound, (some astetic issues and wear and tear, carbs need cleaned, but nothing major apparent), but for whatever reason, one of the cylinder head bolts are off, and it's scaring me off of buying it. A bolt and it's nut is off of the engine, and it seems to have been drained of oil, which makes me think that there was some untold problem that required it take all apart. Any thoughts? Other than that missing, the bike only has 20,000 miles on it and seems to be fine. Is it worth a $650 gamble?