all the pcv valve is is a thin rubber bellows with a very light stainless spring that works is in a way that when inlet pressure drops or increases will open and close the flow between inlet and rocker crankcase as to allow crankcase gases to be fed into the inlet ie to burn off NOX gases, when this happens it also includes any oil that is in the pipe work, what causes oil to be in pipework tends to be where crankcase pressure is to high, what tends to cause this is blow past form piston rings and turbo failure between the compressor to oil chamber in middle of turbo, this also causes blue smoke from exhaust if its exhaust side to oil chamber it tends to be white smoke as oil is not totally burnt it more like spilling oil on a hot surface effect,,, if piston blow past this tends to be due to build up of carbon on rings as if cat gets contaminated with oil or car not driven hard enough as to clean the cat causes back pressure to increase and the carbon has to go somewhere, hence why i use seafoam engine flush in the oil just before oil changes it cleans all this out.