I know there is a warning on the cans that the 'propellant' is flammable. That might be why some tire places won't touch them. I also just found the sensor answer:
"FLAT repair: using a can of pressurized tire repair sealant will clog the sensor and it will have to be replaced."
Tire Pressure Sensor Unit - 2003 to 2005 Xterra
Code: 40700-Z33
Price:$92.88

Ouch! Gonna take that can right out of my car asap!