ls wheel leak ?

The impala that I just purchased looses about 2 psi a day out of the front passenger side wheel when it is just parked. It looses about about 10 on a approx. 20 mile trip (the farthest I've driven it at one time so far and that was mostly highway miles). The tire is about 4 months old with about 7k on it and is the "National" brand tire. It seems to be mounted proper,no damage to edge of wheel, valve isn't leaking, and can't find any punctures. I was wondering if it's possible that the wheel itself could have a slow leak considering I remember hearing somewhere that some other person's late model GM wheel was doing something like this and it was driving him crazy.
I just wanted to know if anyone else has come across this or has any advice-
Thanks-Tim

Dunk it in a wheel tub at a tire shop with about 40 psi look for bubbles, yes an alloy wheel could leak, epoxy can fix it. Or the bead of the rim isn't sealing common in high corrosion areas of the country.