Tire Sidewall problems of the 1996 Jeep Cherokee

All 4 pirelli scorpion st tires, size lt235-75-15 that were purchased 9/02 have dry rot. Dry rot was first noticed 4/04 (19 months after purchase). The tire seller viewed the tires 11/13/04 and is notifying pirelli and will advise me of my options. The tires have 11/32 tread remaining and have been on for 10,000 miles. The dot marking on 2 of the tires are: xl m3 8789 0402 and xl m38789 3901. The dot markings on the other 2 tires are apparently on the inside.

Cracks in sidewalls.