On gasoline engines I have seen Oil get by worn valve guides and stems. But on them they usually used simple deflectors not valve stem seals as they were not overhead cam engines.

In your case I would be thinking work valve stems or guides and the Valve Stem Seals.

Note I also drove a gasoline engine car that had worn exhaust valve stems and or guides where if you left the breather cap on the crankcase pressure built up high enough to cause Oil to come out of the Oil Pan to block gasket area. Driving with out the breather on solved the problem (that was the one on the valve cover). (Note this was in the very early smog emission days.)

__________________
84 300D, 82 Volvo 244Gl Diesel