Before you buy something new, I would contact Otter Box customer support and let them know about your problem. I have an Otter Box cell phone case and they have replaced the belt clip TWICE with no questions asked. The first time, the clip breaking was clearly MY fault; but they sent me a new one anyway.
As a side note, I would strongly recommend the Otter Box cell phone cases to my fellow cachers. I've been out caching in the rain, but my iPhone stays clean an dry in the Otter Box.