Following is from Pressure Pro's announcement of a new sensor seal:
PressurePro's new valve seal solution uses a 2-piece valve seal system. The first piece is a hard plastic depressor that rests on a surface just below the threads. This new plastic depressor has been designed to the optimum length to more fully depress the valve and provides a hard stop during installation, preventing over tightening of the Sensor against the rubber sealing surface; thus preventing damage to the seal. A simple rubber O-ring is pushed into place over the plastic depressor which fits snugly in place and can endure repeated loosening and installation of the Sensor.
No mention of cost to retrofit.
It's about time they did something meaningful . Have (not) had good luck with their older thinking and don't give a toot about it . Brad Metzger
If you search online, the cost for 10 seals plus the "tool" (a modified inexpensive hand tool) is $10
PressurePro Tire Pressure Monitor Accessories (http://www.tirepressuremonitor.com/pressurepro-tire-pressure-monitor-accessories/)
I couldn't find anyplace that sold just the seals or where you could buy additional individual seals (for those of us who need 12 for tag axle coach plus toad).