How long did the OCI's with the oil monitor go? I would expect nothing less than a spotless engine with M1 or any name brand synthetic changed at the appropriate intervals in a healthy engine.
The owner's manual calls for 7,500 so I suspect the OLM is in that neighborhood.
The passenger side head is spotless and valve cover had very minimal varnish. The driver's side head had some yellowing and valve cover had some cooked on varnish. The issue is isolated to the driver's side head and is not engine wide. Peaking down both sides into timing cover revealed a bright & shiny/silver engine.