A friends Mach 1 was eaton swapped, ran great for a few weeks including passes down the 1/4 mile but a week or so ago he discovered his spark wells on his driver side head the back 2 wells at least filled with oil. What would cause this to happen? He has cleaned the oil out, replaced/cleaned/rebuilt the COP and replaced the plugs. He had also installed a JLT catch can. I don't think the oil issue is as bad now but has a misfire. I don't think it's throwing codes either. Over 3k it acts fine along with crusing speeds and under load.