This is an oil flow illustration with a pressurized engine,factor the picture without pressure as in a gravity feed system and you can see that hydrodynamic force does not pressurize the oil.
the previous owner of my engine ran a vent tube from the top rear of the valve cover.This vent tube prevents positive or negative pressure from building in the valve chamber directly above the rear main feed tube..I personally have doubts about the need for it,but left it for it causes no harm.
Oil leak at the radius ball?sure it isnt your shifter shafts leaking?