Before PCV was a blowby tube. The PCV was the earliest form of a smog device.The blowby tube allowed blowby gasses from the engine to vent into the atomosphere. The PCV allowed the engine vacuum to pull blowby gasses from the crankcase into the intake manifold and burn them in the cylinders.The breather on the valve cover allows fresh air to be drawn into the crankcase as the blowby gasses are drawn thru the PCV to the cylinders.If you don't have a breather on the valve cover the system will not work, and pressure will build up in the crankcase and the pressure has to go somewhere. The weakest pace in your sealing system will let go.
OIL leaks big time. Simple solution is vented breather on valve cover and a clean PCV to remove blowby gasses. By the way the PCV opens to remove the blowby gasses and closes to keep the
oil in. It only works off the intake manifold vacuum. Hope this helps.