Tire Sidewall problems of the 1999 Ford Econoline

Noticed 2 seperate cracks or splits on the front left tire of my vehicle. The cracks are on the sidewall of the tire about 1/2 inch each. They are seperate and about a 1 inch space betwween them. But a very fine line or crack can be seen conecting the two from one end to the other. I've taken the vehicle to the firestone dealer at bustleton and street rd. In feasterville,PA 19053 iwas told my tires were not on the recall list , I mentioned that these tires were on the news for blow outs and tire seperation. The dealer then said if the cracks get worse to bring them back and he would reinpspect them but for now it looked minor. Also I pointed out that very small cracks surrounding the diameter of the tires below the tread on the side wall could be seen on all the tires. The dealer said it looked like dry-rot, I then commented that the tires were new with vehicle and purchased 11-98 and only had 11,700 miles on them. The dealer said to just keep an eye on them and if it worsens to come back. After that I took the vehicle to john kennedy Ford where the vehicle was purchased from and told them about the tires. I was told they were not on the recall list and there was nothing they could do and they reccommened to take them to the tire manufacter for inspection. (tiresize: lt22575r16)( dot number: tire size: lt22575r16 ).