[rab60bit]

Rubber degradation - cracking issues due to road contamination, sunlight exposure/UV and irregular use/dry storage are the usual culprits. Avons aren't what they used to be (but then they are not alone) and the rubber mix is something only the manufacturer has control over. DOT code helps but doesn't make you feel better about the situation, none the less still adequate if you don't ever carry heavy loads and/or keep your speeds down to say max. 50mph non-motorway driving. You are likely to suffer slow punctures/leaking before a blow out - but why take the risk.
I haven't had any issues with Goodyears so maybe move to another brand and if you tick any of the above driving boxes as a norm, buy something cheap and replacment costs will drop - who knows they may last the remaining lifetime of your car anyway.