have you thought about a head gasket (the green stuff could be antifrezze)

Yes, I have considered it.  Usually if that is the case, then it would be discolored throughout the engine.  The dipstick oil is black, and smells gassy.  No milky color nor green on the dipstick.  The green could be a mixture of antifreeze, if it were a head gasket... but I'm not sure if I even have antifreeze in my radiator I think it's just water Guess that's my next thing to check out