Condensation from the heat cycle of the engine is the cause.. The splash system ford used creates a monsoon of oil, the rods throw oil everywhere in the crankcase. The valve chamber doesn't quite get the same effect, at higher rpm the oil drain back tube cant handle the flow and oil spills out the front of the block through the punched hole above the timing gear.. the lifters and valves splash it some, but not enough to get past the head gasket hole the shaft passes through.