agreed on valve stem seals. inexpensive but just as hard as a head gasket fix imo.. at least as time consuming.
i would first check your #3 valve cover gasket. #1&2 valve covers.. 14mm bolts and.. erm am i missing anything up there?
a good test is to see if your pushing an air/ oil mix up through your spark plugs while running.. if your pooling oil in your plug galley and see small air bubbles coming up through the sealing part of your spark plug wires.. then yes defiantly valve stem seals
just my 2 cents worth
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