I work at another National tire chain part-time, and we've had some bad valvestems also.
Everyone should have a look at their valvestems.
The good news is that they typically cause a slow leak (as opposed to a blowout), and when the person goes to add air they notice something funny with the valvestem. Of course it doesn't always happen this way, so check your friends' valvestems also.
p.s. [Political rant]: They were made in china [/rant]
I took my wife's car down to Discount Tire as she had valve stems as part of the recall. She actually had a slow leak in one tire. It would drop about 1 psi a day, but there was no visual clue to tell me the valve stem was bad. They tried to sell me a new set of tires while I was there because one of her tires was down to 5/32 tread depth. I can't blame them for trying to make a buck.
yesterday, as I was headed to the Detroit airport on I96, I couldn't control my Explorer so I pulled over. My passenger side rear tire was so low it was about flat. After a good soul helped me change it, I went to the airport to pick up my family. On the way back home, on I96 again, I start losing control again. I had to pull onto the exit ramp at Novi, at RUSH HOUR, and my driver's side rear tire was so low it was flat. I just bought these Michelin tires last year from Discount Tire. My car had to be towed on a flat bed to Belle Tire and they fixed both tires for free and showed me the dry rot...I shudder to think of what may have happened if I didn't recognize the "shimmy" in the steering. CHECK YOUR VALVE STEMS!!
Luckily, I've never had that problem. The tires on Rusty are so old... Lets just say I bought them at Montgomery Ward... I had just put new tires on my Buick about 2 years ago, but the old tires I replaced were about 10 years old. I might have replaced them sooner, but Goodyear was no longer making the wide whitewalls that I used to keep on it.