Doherty Crank Vents?

I've been reseaching these parts for awhile with no explanation as to how they actually work.My guess is there like an automotive "pcv" valve/one-way check valve.Does the vent system from the heads(umbrella-valves)really have the ability to draw air in?I'm confused This product is on my mind due to my on going problem with my rear cyl. exh. push-rod tube o-ring leaking oil.This condition occurs when I'm riding at high speeds for more than a minute or so.The speed range is between 85-to-110MPH(I know this is not safe & don't advocate this driving style/just stating the facts of my situation).Since the beginning of this problem I have vented the head manifold pipe to an external "K&N" style filter...Problem/center tube o-ring still blows oil out at high speed jaunts.I hope one of you out there can help me resolve this...If anything,Thanks for listening.00 wildglide