While it is not "normal" it happens frequently.

The Hydras on our 744 TI leaked 5 psi, per week before we got new tires and had the wheels cleaned.

If you look at an unmounted rim, you will see that movement of the tire bead has taken all the paint off in that area.

We had a set of steel wheels that rusted in the bead area because the sleezy tire dealer that sold the tires to the last owner used a gooey sealant. These wheels had to be discarded because there was 1/8" of rust under the bead.

You should have all four wheels cleaned in the bead area.

I check tire pressures weekly because of problems such as these pop up if you drive 10-year-old cars.
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96 855R, 95 855,854, 90 744 Ti - 340,000 Volvo miles put on 7 bricks