A few days back, the low tire pressure light came on, and I checked that the LR tire was only about 20 psi while the other three were ok (>30). I inflated LR to ~35 psi and the others as well. The warning light disappeared. Today while I was filling gas, I checked the LR, and it is already down to 30 psi (hot) whereas the other three were about the same. - Is this just a small leak/puncture or something else (valve stem, etc)?
Cross your fingers it is in the treaded area and not on or near the sidewall or else it cannot be fixed safely.
If you want to check for yourself... With the valve down put some oil in it, if you see bubbles it's leaking, use a valve stem tool and remove it. clean it, oil it and reinstall it, air up and check it again. Unless of course you find a leak in the tire. Take the wheel off and rotate it in a large vat of water, the bubbles will show the leak. IF it's patch-able, have a pro do it (you have to remove the tire from the rim). If it's not patch-able and if the tires have much wear you'll have to replace at least two, possibly all four, sad but true.
I'd personally not put oil on a TPMS valve. Soapy water, maybe. You could also spray soapy water onto your tire to locate the leak--that's what the tire shop would do. How to Find a Tire Leak | eHow.com It's most likely you've got an easily fixed puncture, but you need a tire shop to fix it.
Soapy water is the preferred way to check for air leaks on just about everything. I had an issue with the valve stem leaking on one of my Dodge's TPMS sensors, and I just dealt with it till the the tire change so it could be rebuilt. Also check the tread area for any small pieces of nails, and things of that nature. They recommend not patching tires, but I do it whenever I get something stuck in there with no issue.
