2012 Civic - one tire loses pressure

My Honda Civic SI is a cute little car with almost 70,000 miles. But it has one annoying problem. Every four to six weeks the “low tire pressure” warning comes on. Usually the left rear tire is 6 to 10 pounds lower than it should be. The right rear tire is down, but only by a few pounds. The front tires typically are fine. This has been going on for several years, summer and winter, through several winter tire changes. Neither the tire store I use or the dealer has been able to identify what is wrong. Any thoughts?

Nearly all tires leak a tiny bit. Some more than a tiny bit. Sometimes porosity in the wheels can be an issue. Sometimes corrosion, sometimes leaking valve stems. Sometimes it takes new tires. sometimes you just have to live with it.

At least the TPMS is getting you to check and fill your tires regularly. Seems like it is doing its job.

I say buy a good tire gauge and pick a day ( Saturday ? ) and just check them once a week . I check mine on the 15th and 1st of each month . But mine don’t lose much air.