I changed the plugs on my M last week and plugs from #2 and 3 cylinders had some oil residue but cylinders 1 and 4 didn't. I'm assuming it means something in common with the 2 cylinders. Wondering where oil is leaking by. I also got about a 1/4 cup of antifreeze when I changed the oil. The old tractor still runs OK but I have owned it since 1988 and have done nothing on the engine. I don't know the history but given what I see for power it is about what I would expect from a stock engine so either someones rebuild is worn a lot or maybe the tractor has never been overhauled or maybe overhauled in the past but not upgraded for horsepower.I'm thinking of pulling the head for a valve job sometime in the near future but when I do I need to be prepared to spend money on a replacement if I find this one cracked.Probably be a couple of years unless the situation gets worse.It is on my bucket list of things to do before I retire in a few years and won't want to spend as much big money on tractors.