I do know on a 2012 Subaru Forester there is a part called the PVC Hose Connector (which isn't the PVC valve).  It is a connector with 2 hoses -- one is water and one is a breather hose (vacuum).  This will leak oil residue into the water if the o-ring is bad.  Poor design to put those 2 hoses on the same piece of plastic.