I just had a set of new tires put on my 2015 LS460L AWD and had the tire pressure monitor notify me of a leak. I thought that I'd picked up a nail and took it back to my Discount Tire shop where they found no nail (good thing), but found the leak was from a tiny hairline crack on the inner bead ridge on the wheel (bad thing). New 19" 7-spoke alloy wheel lists for $640.08 (Part # 4261A-50162) and is available from several Lexus dealers online for $461.78, plus shipping. I found one on Ebay with a full-price return guarantee and bought it. Looked good when it arrived and I took it to Discount to have my spare remounted and put away.

 

Thanks, hope that does not end up being the problem. Mine are $1900.00 each or 1350.00 from a dealer online. Since mine are the sport model.

 

Another option to try is put some tire sealant, fix-a-flat, in there to stop the small leak.

 

So ended up replacing all the valve stems / TSPM sensors with OE. That seems to have fixed the problem. They were about due for replacement anyway.
They did of course remount the tires. And guess it was still a small chance they were not sealed against the rim well. Looks like they used rubber cement this time and not sure about the last time.