I disagree. The valve cores on my 04 started not to snap back up/seal all the way after checking the tire pressure. After I pushed the guage down on the valve stem and released it the valve core would leak until I pressed it in and out a couple times with a finger nail.
Are you sure the valve cores were tight? Sometimes if the cores rotate loose, they can seem like they are sticking. And if they are loose enough, they will definitely leak air.
I had new tires put on at 89k and also had the TPMS sensor serviced.
What do you mean by "serviced"? You can't even change the batteries in Toyota's TPMS sensors, so I'm not sure what type of service you're talking about.
A good tire shop will have the proper valve cores and even the nut that holds the TPMS sensor to the rim from the outside in stock. Valve cores have a rubber seal in them and it will dry rot over time. I had mine put on @ Discount Tire. They did charge extra to do this, maybe $10/wheel. I have had no problems with the new cores sticking since and it has been about 3.5k miles since they were changed. I also check my tire pressures every 2 weeks.
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