For anyone with the TST TPMS 510 System --A little more trivia:
I found out that the older 510 system sensors have had a silent upgrade. The sensors they now ship for that system have had the seals changed. They are now black rubber instead of the clear material that was in the earlier sensors. The clear seals were not replaceable and when they would not seal it required a sensor replacement. For the newer ones the black rubber seals are replaceable and will be provided by TST upon request -- at least that's what TST told me
They also indicated that they will replace the older sensors with the new ones for half price.
Tim