Amazingly 'it's only the first failure we've seen like this' becomes a standard reply!
Who me, worry about a cracked rim????!
We've cracked about three Mavic MA40 rear rims, and then only after 15,000 to 25,000 miles on the wheel. And yes, Mavic replaced them and they were surprised we got that kind of milage on one of their rims on the back of a tandem. Rear wheels of course really get torqued pretty hard. We had one MA40 front rim last 56,000 miles on the front of one of our tandems . . . and for all we know it's still in use as we sold that bike when we bought a new one.
It pays to go over the bike/components with an eagle eye every so often . .
Pedal on TWOgether!
Rudy and Kay/zonatandem