run flats 20" for the x6 2012 year

Has anyone had any issues with these tires...I have just put the 3rd set on the front of the car! Dealer's set, wore due to improper alignment of the rear! Fought with the dealer and gave up. Had a major alignment with new tires, same run flats that came on car. Noticed a slight bulge on the sidewall that ran up the the edge of the tread...there was only 4,000 miles on them.Took it in, they indicated as normal, I must have hit a crub! Well after agreeing to purchase new tires, they started the installaion of the tires...The tire with the bulge! it had a 24" long crack on the inside of the sidewall....There was no damge to the outside sidewall, no crub hitting. I am concerned that should that tire had blone out and the tire shredded..They would have never found the defect of that tire on the inside! I did get 2 new tires from Firestone with the roadhazarded coverage! Anyone have any knowledge about these tires being defective! 2012 x6 5.0 20" Y spoke

Thankyou!