When I recently dismantled the valves on mine there wasn't an o ring in the inside of the wheel just the seal that seems to be part of the stem. The outside part that screws onto it had a seal at the bottom of it which again seemed to be part of it so that the wheel is sandwiched between two rubber seals. There definitely wasn't a loose o ring, just the seals that seemed to be part of the assembly. I can't see why there'd need to be an extra o ring.