Past few weeks rear driver side tire seems to want to settle down about five PSI below spec. I kept putting air in and it would be good for day and then seem to magically drop five PSI. Even stopped by Costco and filled the darn thing with nitrogen. Still lost air. Was all set to head for Les Schwab tire shop and have them look for the slow leak when my slow mind had an "Ah Ha" moment. I dug out my little valve stem tool and tightened down the stem. Three days, no leak. I will blame it on what my elderly mom used to call it -- Old Timers Disease.
The original Toyota TPMS sensors (Pacifica) have these gray caps. I noticed there's a red gasket inside when I was airing up my tires during a cold snap. One of the gaskets stuck to the valve stem rather than staying inside the cap. This gasket could also help seal if you've got a leaky Schraeder insert. I'm sure trying to keep the original caps, and them being intact would prove to be impractical. You'd be fighting an uphill battle against every tire or other type of technician that removes those caps on your car. There are probably aftermarket caps that have gaskets inside, but they're not the ones at the dollar store, Walmart, auto parts stores, or the ones the tire stores, or "quicky lube" are going to put on your car when they're finished doing whatever, either.
Ancient history, but back in late 1970s, early 1980s, a woman I dated had a Toyota pickup. Tires had grey valve caps. I still have a couple of them in my tire tool drawer...I will admit it...When we entered our long break-up phase, in an act of childish pique, I stole all her valve caps. Yes, still feel a bit guilty about such an immature act...but I had done about $500 to $1000 work on that truck, tune-ups, ignition cables, shocks, water pump, thermostat, plugs. And that was 1980s $$$ Several years later, saw her at an industry event and admitted my crime. She laughed and said she wondered where they had gone. Actually, surprised she noticed (sort of doubt she did).
