Tire Sidewall problems of the 2006 Nissan Titan

Tire sidewall separation. On 4/25/2009, I purchased 4 new toyo open country h/t, p265/70r18 truck tires for my 2006 Nissan Titan pickup truck. On Sunday, 5/3/2010, I noticed the right front tire had a small chunk of the black outside sidewall missing. Upon inspection, I could not find where any type of debris had hit the tire, nor could I find where any of the other tires had been damaged. The following day, I took the vehicle back to the dealer to have them inspect the damage. At the time of purchase, the total vehicle mileage was 30,586. As of this date, the mileage is 40,845. A total of 10,259 miles have been driven since the tires were purchased. As the tires came with a 60k mile damage warranty, I was expecting to have the tire replaced and to pay any mileage adjustment fee. The dealer instead informed me that, because of the type of damage, they would have to contact toyo and obtain their approval to replace the tire. I was told until toyo contacted them, there was nothing they could do, but that it was safe to continue driving the vehicle. I have contacted the dealer regularly, and have told that toyo has yet to respond. After checking the ntsb. Gov website, the only recall for a tire close to the one I have mentioned is a toyo open country a/t model.