Does anyone have experience with wheels aging out? I know this is a subjective question based on type of wheel, use, care etc. But we're not talking F1 wheels that are used once.

The wheels in question are 14x7 Borbetts from a 1.8L Miata that sees use in HDPE events and long enduros only. We had 12 wheels, all purchased at about the same time and all used equally since then. In 2007 we found one w/ a cracked spoke so we scrapped it and looked at the remaining 11, they all looked fine. I was dismounting tires off of them this week and found that 5 of them have what look like hairline cracks on the backside of at least one spoke.

Has anyone had wheel failures that were not directly related to contact w/ something more than a track curb? Anyone ever felt their wheels were simply too old to be reliable?