[VegasDelta]

Remove all the plugs, check compression in all cylinders & write down the results. Low compression in adjacent cylinders usually indicates a blown head gasket. If readings are low overall, add a tspn of motor oil to each cylinder as you re-check the compression. An increase in compression indicates worn rings, no increase indicates worn valves.
A blown head gasket can sometimes cause oil in the radiator or water in the crankcase. Good luck.