Originally Posted by
bmorgil
I think you are on track. The clean plug is classic of a "steam" cleaning that the plug gets when water begins to enter the combustion process. I think it is a head gasket also. It has good compression for cranking and fairly uniform. Typical for a head gasket that is just starting to go. The fluid present in the leak helps make a seal. The way to be totally sure is to put a pressure checker on the cooling system. If you put 10 psi or so on it I bet the water leak will show up. If the head gasket is leaking it will not hold pressure for long. Also when it is running you should see bubbles in the water. Running the motor with the radiator cap removed, look for bubbles in the water flow once the thermostat opens.