[John Rogers]

That little plastic thingy is the PCV valve. Should be clean and free to move. The gasket on the bottom of the oil filler assembly should be a good seal and you might have to bend the wire bale to get it to fit tight. On both of our Porsches, the vents go to the air cleaner, downstream of the filter so there is a slight vacuum effect and the fumes are then burned. The pressure at the filler can be caused by blow-by and insufficient crankcase venting. Try larger, separate hoses and crankcase pressure should go down.