I've had the same problem with my '05 since I bought it. Didn't realize it was doing it for a while. I've looked for a bent rim, a crack in the wheel, I've asked the stealership to check the bead a few times when I've had rubber swapped, and changed valve stems and stem caps. No joy.
Now it's just a matter of adding 5lbs psi about every 3-5 days. Oddly enough, there are stints where it doesn't lose air and others that it loses 15+ in a week. I chalked those up to temp changes or something of that sort.
It's a PIA fo sho!