If it is blue like you say then you are on the right track, oil related. Since the valve covers are off, inspect the valve seals to see if they are damaged or missing. Simple thing to check without pulling the head. A damage seal will allow oil to leak down the valve stem and into the combustion chamber.
I pulled the left side valve cover off to check the valve seals. It was not easy to see thru those dual springs, but as near as I could tell, there was no obvious problem.
Thanks for the help,
Art
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