Inside tire valve extensions

Went to get the motorhome out of our storage garage today. My TPS system usually takes a minute or two to kick in once driving. The low pressure alarm went off. My motorhome says to keep tire pressure at 90psi but I normally keep them a few PSI above 90. My right rear inside tire was indicating 62 PSI and the other 5 tires were between 93-96 psi. I only live about 4 miles from my house so I drove slow and parked in the driveway. I have a big air compressor in my storage garage but I have a small one at the house. I was able to get the PSI in the low tire up to 76 PSI with my little compressor and drove slowly to a local tire place that does truck tires.

As soon as the tire guy came out, he said your problem is probably that tire valve extension. He said 90 % of the time, a slow leak on an inner tire is because of the valve extension. I don't know if he tightened the extension or put a new one on but he said its fixed now (so far PSI is the same).

Is this a common problem? If so, what is the fix? If there wasn't an extension I am scratching my head wondering how you air up the inner tire?

I guess I will know if the issue is fixed tomorrow but so far PSI hasn't changed on that tire since it cooled down from the drive home.

Burch