Servicing a Tire Pressure Monitor in a TPMS

I have tried to research this.

I've called the Toyota dealer too, and they said there is only a gasket and valve cap that can be serviced.

I've even gone on to the Tundra Trucks forum, where I read
need info on Tire pressure monitoring system - Page 2 -

But on Untitled Page it lists "Toyota TPMS Service Kit D1100K" which states, "Each kit includes: Valve Core, Valve Cap, Grommet Nut and Grommet."

So who is right? Does a service kit exist and Toyota isn't selling it and hoping you will buy their $100 Tire Pressure Monitor if there is a problem?

Also, have people found that these TPMS valve stems will leak? I have a tire that loses about 2lbs pressure in a day, but then seems to stay at that pressure. I had it checked at a tire shop but they could find no problem. (Oh, and the reason I found out about it was because the TPMS light came on, I checked the pressure and it was very low, around 20lbs. But now that I've been filling it up to 40lbs it seems to never get lower than 38lbs. This is on original Goodyear Integrities with just over 25K miles on them.)