It does come down to the point that are the cams getting enough oil? I bet most of us on here can hold our hands up and say we have had a worn cam. Now surely kent, piper and newmans can get it wrong. My way of thinking is are the oil pumps up to the job? How old are they? Are they worn? The other thing that goes through my mind is can the oil ports be opened up in the head to have better flow?