Excess Crankcase Pressure

FIRST thing I'd do is make sure the PCV is actually "sucking" and make sure nothing is plugged. Take a scrap clean hose so you can blow through the complete breather hose.

When idling, remove the breather. Observe what is going on, IE fumes exiting or not from the filler port. Now remove the PCV from the rear breather and see what difference it makes. You can place/ remove your finger over the PCV and should immediately be able to tell if it is opening and closing and has "suction" going through it