Hi Tom,
Are your 2013 tires Michelins? If so, you may want to call Michelin consumer care and complain. They will ask you to go to an authorized Michelin dealer to get a warranty adjustment. I work for Michelin on the OE team and we changed our warranty to include ozone cracking.... when the warranty changed, we grandfathered tires already in service. Tge credit is generally based on remaining tread deoth, so you should get a good discount on the replacement Michelins.

If you need any guidance, my official email is pat.meisenholder@michelin.com