I purchased a 1999 miata as a project for my son and I. Perfect body, but it has motor issues. 200,200 miles It was leaking coolant and smoking (smells like oil) when we bought it. I found the coolant leak. It's the o-ring on the return line from the heater core. As of right now I think that is the only leak. The motor is covered with old and new oil. The timing belt has been replaced, but the cam seals, crank seal and CAS may have not been replaced and possibly still leaking. The spark plugs were wet with oil. Compression test shows: #1:160, #2:165, #3:155, #4:170. Wet tests were 185-190. Leak down shows zero leak on all cylinders. The intake has oil in it, I believe from the PCV valve (I removed the top half of the intake). I'm unsure if the valve guide seals are good or not? I'm fully capable of removing the engine and rebuilding it. I'd prefer not to, if I don't have to now. Is it reasonable to replace the o-ring on the coolant line, and replace the PCV valve, put a new valve cover gasket on and see how it runs? Power wash everything and try to determine where the leaks are coming from? Or is the a better route to take at this point without removing the engine? I appreciate your thoughts and suggestions. Thank you Matt