The rest of the story:
I called Car-X back and told them since they don't carry the rebuild kit, to just leave the TPMS sensor/stem alone.
They did tell me that there was a bead leak as well, they dismounted the tire, cleaned the bead and rim, gooped up the bead with black sealer, remounted the tire and re-balanced it. (Why they just didn't put a mark on the tire at the stem, and then simply remount the tire in the same position.... never mind... too much to ask I guess).
When I picked the tire up, the guy that worked on it in the shop was at the front desk and made the comment to me "It'll probably be flat in the morning, and you'll be back..."
I found that to be a odd thing to tell a customer... but whatever.
Went home and put the wheel back on. And as was predicted, it was sitting on the rim in the morning. So, Car-X took it from losing less than a pound a day, to going flat overnight.
Out of a hunch, I then checked the nut on the stem, and it had been left finger tight. I should have checked that sooner, but I didn't think it would be necessary. Found the specification online, tightened the nut accordingly, and pumped the tire back up.
I now find the prognostication about it being "flat in the morning' quite disturbing, considering that the nut on the valve stem was only finger tight. Either it was an intentional move since I didn't shell out $75 for a new TPMS sensor/stem, or it was the world's sloppiest mistake.
Either way, I'll never go back there.