I agree with you mcparadise. The only point on which I would like to comment is the one about additives.
Purchased separately, additives are a waste of money. However, Amadameus might try an oil with a different additive package already in it, like a “high mileage” oil. It couldn’t hurt to try.
Amadameus, replace the PCV valve, let us know how much oil is being burned, and give us the current odometer reading.