To be honest if you have
in the header tank, then i would also say its the dreaded head gasket. HAve you checked the
dipstick ?? i think you will find a milky sludge at the bottom, all the problems do seem to relate to this.
I did a quick google check on your problems, and the running on problem you have also seems to be a symton of a blown head gasket.
This is taken from another site .......
Question: My car is trying to keep running after I shut the key off. What would be causing this
Answer: Your problem may be that your idle speed is set too high. Correcting to the proper specifications, should fix your problem. Also, check that your car is not overheating. Sometimes, too low octane gas can be the culprit.