Similar thing happened on my TREK SU100, which I have since sold off on Craig's List,
I bought it new in 2006 and a year ago it split at the production seam, lucky for me, I posted pictures and a short story about it on this bike forum, I found out from one of the viewers that Bontrager has a 5 year warranty on the wheels, took it to the Trek dealer, and a new rear wheel was ordered. no charge.
What's the Marin warranty like????