Tire Sidewall problems of the 1999 Nissan Altima

Upon routine inspection of the tires, it was noted that there is a crack running around the circumfrance of all four tires where the tread meets the sidewall. This is on all four tires. Our dealer has recommended that we replace the tires before warm weather starts. We decided to investigate online to see if there was a recall on these tires. There is no recall, but there are numerous complaints listed for these firestone affinity tires for tread separation. I feel there must be a manufacturing problem with these tires. Thank you for your help.