Check the easy stuff first, being the PCV system. I had a kinked hose in my PCV sytem that was causing a similar problem. I replaced my valve cover, rear main and pan gasket before I realized that the oil was coming from the dipstick tube due to the crankcase overpressurizing. Turns out that one of my PCV lines had gone soft over the years and kincked closed on one of the bends. Looked ok untill I completly removed it and looked inside. A new hose and all was good.
I don't see how an oil pump wiould help.............