There is oil in this area because system it not just a ventilation it's a oil separator. It separate the oil from the vapor returning the oil back to the crankcase so the return side will have a large amount of oil pudding in the valve cover port. Due to the amount of crankcase pressure these engine creat vapors that carry oil with the vapor that's why in some cases when ******** this system with some aftermarket system customers report oil consumption they created the oil loss by removing the engines ability to separate the oil from the vapor so now oil and vapors are vented to the ground or exhaust system depending on design of system. In most cases it gives the truck a nice rust resistance under coating from all the oil be blown out the valve cover vent.
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