Yeah, I thought it might be the valve stem as well considering that the metal part pulled right out of the valve stem the last time I tried to blow up the tire. However, when I was trying to break the tire seal around the rim, I noticed quite a lot of cracks in the rubber down near the rim. I ended up reglueing the metal guts of the valve stem back into the valve stem and reinflated the tire. Unfortunatley, the rate of deflation was unaffected by my valve stem repair job.