The model is a c40mb-193-782. It is a flathead. It is a unit that would have been started and stopped in short periods and maybe condensation is the answer, I hope. I see no white smoke, or moisture, out of exhaust. It runs very good without skipping or noticeable audible differences in firing, however, very milky look to oil and lots of moisture on oil fill cap. Last night after running for ten minutes and opening the engine compartment I could smell antifreeze, I don't know if that is a hint but that is what I noticed.Would it start to skip, or could you hear the difference in the firing if the gasket or block is cracked? Is it hurting it more to run it, if in fact, it is a head gasket? What should the plug compression be, I suppose you are looking for an unbalance from one to the other. Any other telltale signs to look for? Are parts available for old Clark forklifts and where would I start to look. Thanks a lot, I appreciate it as I am a new user of forklifts. Regards, Mike