#30 is the differential pressure valve. it's the most likely cause for this problem. What's inside is a rubber diaphragm that controls the passage from the breather tubes to the intake manifold. If the rubber has petrified, it won't open, which allows blowby pressure to build until something gives...the rear main, the dipstick, whatever the weakest seal happens to be.

Do not let this vent to the atmosphere. Aside from the legal and social implication of releasing contaminates, it's like venting your exhaust into the engine compartment. Eventually, it finds it's way back into the passenger areas. A third to half of all engine pollutants are eliminated via the crankcase breather.