I have a pair of goodyear assurance all season tires on my vehicle that are 1 year old and has 4,000 miles on them. I noticed small and many hairline cracks between the treads and my mechanic refuses to warranty them out claiming its normal and because of heat. I attachded some pics, what do you BITOGers think? I must add they have no drycracking on the sidewall. Thanks..