I pity the people that own the little Clark (G127) with the Mitsubishi motor. There is a oil galley that comes up through the head gasket on the left side by #4 cylinder. I've fixed 2 of them that had the oil pouring right out of the head gasket next to that galley. I suppose oil could leak the other way into the cylinder. Maybe check the spark plugs to see if they are all uniform. I have one customer that has had this head gasket problem, cracked both tilt cylinders, lift cylinder leak, brake overhaul needed (who designed that master/inching cylinder set up?), starter and alternator gone bad, and fuel system failure. One problem after another. After putting on a perfect reconditioned head it still puffs a little smoke when started and when you floor it after idling a while. But this machine has a lot more than 2000 hours. I wouldn't rule out the valve seals. If it ever got overheated, I think it hurts the seals.