hmmm... you don't really understand motor do you?
the only pressure in the valve cover would be fromo the rotation of the motor, specifically the air thats displaced in side the crank case as the piston comes down... your PVC valve is meant to recirc this air back into your intake
so basically no, the "loss of pressure" is not affecting your motor
its the oil on whats should be clean electrical connections ie: your wires and plugs...