Tire Bubble problems of the 2008 Mercedes Benz C300

Right front tire was replaced at 20k for bubble that formed on the side wall after hitting small pot hole; right front tire needs to be replaced now for the same reason.

The contact owns a 2008 Mercedes Benz C300. She had to replace five tires. The five tires that were replaced also included the new tire she used to replaced another tire. The first incident occurred on may 14, 2008 while driving approximately 25 mph making a right turn and the right rear tire side wall split. And on March 13, 2009 she hit a pot hole and noticed that the right rear front and left tire failed again, they both had a bubble in them. The third incident occurred on February 28, 2010. She hit a pot hole and again the left front tire blew out. She will take the vehicle to the dealer to be inspected. The tires that failed were manufactured by continental, line conti pro contact, size 225-45 r17 91h, dot 65typxh6 all tires had the same dot number except one dot number was lm7rpxh6. The vehicle failure mileage was 1 and the current mileage was 25,000. She contacted the tire manufacturer, but they didn't offer any assistance.