I wonder too. It spit some oil out the tailpipe so I thought maybe the oil passage just in front of the number one cylinder might have been breeched to the cylinder. That semi breech if there will get worse.

I was also wondering if that partial breech might be lowering compression enough to seemingly miss. Hope I am wrong. I would drive it as it will get worse and easier to establish or eliminate as the primary issue. He may notice oil consumption picking up as well if that is the fault.

Sooner or later those engines will probably require a head gasket for that oil passage proximity to the cylinder.