Tires, Rims and Beading

I have a 1999 Chevy Lumina LTZ. The front two tires have always had very slow leaks in them, until I complained enough to my dad. He replaced the valves in them. A month or so later, I suddenly have accelerated leaking. I always kept up, never rode on my rims, but it was enough to push me to take my car to a tire shop a few days after this.

I explained to the guys there that my suspicion was that it was either the valve or the beading. They looked at it, and when I (finally!) Got my car back, they explained that there was no charge, that the problem was in the beading and they couldn't fix it -- they cleaned corrosion of the valve and the beading and nothing could be done. When I asked why there was no charge, they said "Well, we hope when you replace your tires, you'll remember this and come to us."

It's been a few days, and there's no leaking (knock on wood). I have a feeling I was lied to because fixing the beading isn't nearly as costly as replacing tires. Wouldn't "unfixable" beading be a problem with the rims, and not the actual tire?