Oil coming in from the top has probably gotten through the valve cover gasket, specifically the little part that seals out the coil pack to plug hole. You will want to clean everything out, change the gasket and run some good gas in it to clean it out. You are probably running at least a bit rich right now to compensate for the oil. How many miles are on your forward 02 sensors?

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2001 E53 3.0 5pd