Slow tire leak

My coach has 22.5-inch truck tires and doolies on the back. I also have tire pressure sensors on each one of the 6 tires. In five years, none of the tires have needed repair but the inside rear on the driver's side started to leak air ever so slowly. This began about 10 months ago, and it consistently lost about 5 PSI a week. Suspecting the sensor to be the cause, I tried swapping then, removing them and caping the valve stem. Nothing changed. This became and real annoyance and drove me to getting help from a truck tire repair shop in Pueblo West Colorado. After 30 minutes of spraying soapy water and close inspection a tiny bubble appeared in the connection between the valve stem and the valve stem extension. Had I only thought of that I could have saved $72 but now I know and maybe you do too. These extensions just screw on the valve stem, and I expect that I loosened it by twisting the sensor off when it needed a new battery. The owner of the shop said these extensions are notorious for leaking and recommended leaving it off and deal with the inconvenience of having to reach between the wheels to remove the sensor. I may opt to replace the 6-inch extensions with shorter ones but for now the tire is holding air.

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