Leaking Tire valve stem

This is so strange. I have 1 leaking tire valve stem on my XJ. It leaks at the base, where the stem meets the rim. AND my girlfriends car has 3 leaking air stems at the same place. My tires are less then 500 miles old and hers have only 2000 miles on them. Both sets mounted and installed at different places.
But never in my life have I ever seen this happen on two vehicles with new tires on them. Both purchased, mounted and installed 2 months apart. Also, I have never had a leaking tire valve stem at the mounting base near the rim.
Is there a bad rash of tire stems floating around or something? This is getting ridiculous.

Maybe the place that you had the tires changed at did not put new ones in? Maybe they said they did and did not? I have leaky valve stems, I payed a guy $5 to pop the beads on the side with the valves, cut out the old ones and put new ones in. Filled with air and all is good. So $5 + $2 (stems) and they are fine.

You can go back to the place you had them done and complain?
Good luck
katarn