The head gasket could be leaking between an coolant passage and the oil returns from the head. That's an easy fix. It could also be a cracked water jacket. I would suggest pressure checking the cooling system. It should hold steady pressure if it is not leaking. I would also suggest dropping the pan and checking the block internally with pressure on the system for any leaks/cracks. If nothing there, then pull the head and inspect the gasket.

Bill Burmeister