I replaced the valve stems and extensions on our 2552 with Borg Duallyvalve stems because I had damaged one of the original extension mounts. I drove a little too close to the edge of the road in Yosemite and something pulled the L-bracket that holds the end of the extension off of its rivets. I ordered a set of Duallyvalves from
http://www.yourtireshopsupply.com, which is Borg's web site, for $120. I had my local tire shop install the stems. Below is a picture of the stems installed on the wheel (I hope).
The tire guy had a lot of trouble getting the wheels off the axel; they were rusted on. He had to use what he called "Love". I think that involved a hammer.
These stems work much better than the old extensions with my pressure gauge/filler.
Borg also sells stems for the front wheels, if you're interested.