general problems of the 2000 Oldsmobile Silhouette

Bridgestone b420, 215-70r15 tire => tread appears to be separating from body of tire. Tread still plentiful. Engaged firestone corporate on 2 occassions to learn how I can have tire assessed to determine if manufacture\\'s defect, and on both occassion they couldn\\'t assist => told that since tire was sold by sears (I. E. Made for sears retail tire stores only) that sear would have to assess / warranty tire. Firestone could not provide me name of appropriate \\sears\\ contact. How should I determine if tire has manufacturer defective if manufacture is unwilling to look at it?.

Since purchasing this vehicle on March 2, 2001, we have had three blowouts with these firestone original equipment tires. The first one happened before the car had been driven 2,000 mi. This tire had to be replaced by owner - dealer said it was not covered by the warranty. The second blow-out happened at approximately 8,000 mi. And that tire was able to be fixed. However, last evening we had our third blow-out and the tire is completely "shot" and will need to be replaced. I believe there has to be a defect in the tires; we have never had blow-outs in any of our previous vehilcles/tires. (dot number: fr680 tiresize: p21570r15).