You might have a worn exhaust guide in #4. Sounds like oil has been traveling down the guide and "splashing" the plug. It might be okay when she's working, cause' the RPM's are up, but when she idles for a short period of time, she looses oil control and fouls the plug after a while. Excess oil gets pushed out the exhaust manifold, and that could be what you see dripping out between the head & manifold. I would think if it was a ring problem, she would be pushing some serious blue smoke out the stack and running lousy. You not only loose oil control, but you would also loose compression which would greatly have an adverse affect on engine performance.... Steve B.