I remember seeing that and thinking it was a bit strange then. The reed valve only has a pipe from the top of the oil tank with an air/oil mix, as it is part of the breather system. It doesn't hold back any head of oil from the tank when the engine isn't running. The oil pump always has a feed to it from the bottom of the oil tank, this has a gravity head of pressure when it's not running. Any small leak through the pump clearances will eventually drain back through to the oil pump pickup scavenge area, which is the sump. There are no NRV's or shut off valves to prevent this happening, they would just cause more problems. That is just me looking at the diagrams of the oil system, I could be wrong?
