just bought an 06. Has oil sitting on top of coolant in resivior. Not milky, pure oil. No sign of milkshake look. No sign of water in the engine. Is there another answer than head gasket. Any other way for that to happen? 177k on motor, no background on PO, as i bought at auction. Thx for any help on this. Btw, the car does look loke it has been sitting for a few months , not sure if that means anything.