Case 646 blowing oil

[MattMih]

Hi Guys, I have a Case 646 with the original Onan 16.5 CCKA (1975 I think by the S/N). It blows some oil out of the right cylinder muffler and the air cleaner looks oily. The exhaust is also way cooler and bluish on that cylinder compared to the other. Could this be because of bad intake and exhaust valve gapping? Or, would you say it is more likely to be rings?

thanks for your help

Matt