Corrosion on alloy wheels causing leak?

My passenger front tire looked low and I measured about 28 PSI. I usually keep 35 PSI in the tires and have never seen them drop below 32 PSI (except for punctures). Discount Tire found no leaks and said the leak was from rim corrosion. They said they temporarily the rim. However, they said this would not last and the alloys need to be replaced.

First, I'm curious how a 2002 California car would develop this problem. Car is kept in good condition, washed frequently and Discount Tire handles all tire service. Second, how else may I address this problem. I'd prefer not to replace the wheels (they still look in great condition).

Vehicle is a 2002 Mazda Protege ES 5spd with 106k. Alloys are factory Mazda that came new with car in 2002. Believe they are 16x5.5 with 205/50/16 Bridgestone RE750s on all corners.

Thanks! Matthew
Fairly common for the aluminum rims to corrode. Our place cleans up the corrosion and applies bead sealer to the affected area. Usually dodge/Chrysler has this problem with their mags.

Same here in road salt country, one chore I job out as don't have a tire changer in my garage and don't want to buy one. Ironically, my Wal-Mart store does a very good job, lasts 4-5 years, was around six bucks a wheel last time, remove the tire, sand the rim and use a bead sealer. Not recommending Wal-Mart as I know the manager of ours, and he is good, can go to another one, and be very unhappy. But was also told by another tire dealer in town that I needed new rims, he sold rims by the way. My store even threw in a wheel balance.
I've seen this problem on some tires. The air is leaking past the bead between the tire bead and the rim, as the tire ages the tire bead becomes really dry and it doesn't seal the rim completly. So what I did is to demount the tire and clean the rim or use a very light sand paper to clean the edges of the rim where the tire bead touches the rim and apply multipurpose grease and inflate the tire to normal Psi. For this process you need to have a tire mounting device otherwise you need to find a way to break loose the tire bead from the rim.
Sometimes the leaking might be on the tire valve, you can check this very easy using soap and water and apply to the valve after taking off the cap. You can also use soap and water and apply to every place where the tire is leaking and you will see air bubbles coming out, anyways hope this helps!
Ha, I use to pop the bead with a bumper jack to let you know how long ago that was. Angled the base of the jack close to the rim tire joint, but had to use the bumper on my motorhome, a car would just go up with the wheels off the ground without popping the bead. Then turn the wheel over and do the other side. The sides of the tire had to be pushed in that it didn't want to do so the tire could be offset, then came the crowbars to slowly work it out. First side was reasonable, other side hanging free was far more difficult. Putting the tire back on is even more difficult. Ha, never again.

Now rear inner tube type rear tractor tires were easy, and would cost a small fortune for a guy to come out to change those, that was well worth the effort.