well from what i've read, and take with a grain of salt... if your PCV is leaking... then oil/waste could be flowing back in to your engine. the PCV is supposed to keep it clean... I would double check with someone more knowledgeable than me...
On a side note, i noticed when i changed my belts (serpentine and a/c) i got way better fuel mileage. I am guessing the serpentine had more to do with it than the a/c.