Using a neighbors old D4/955 loader (no idea how old but the closest thing I can find on machinerytrader.com is a 1960 and this one looks older yet) to clear some trees and it is getting water in the engine oil.

Had been using it for a while the other night and it was starting to get warm. Shut it down, radiator has a slow leak and was a little low but was far from dry.

Never thought much of it just let it cool overnight, next day checked the oil (looked fine), filled the radiator, started it up and used it for a couple hrs. Saturday checked the oil and it was a little milky, used it for a little bit, checked it again and it was a lot milkier.

 So for any Cat guys out there what likely happened? cracked head, block, head gasket something else?

Any guess to how rediculously costly parts for this old of machine would be? I'm guessing Cat is the only place to get parts or is there aftermarket/salvage yards to check with?