I had the same exact problem. If you bring it in to Shimano in Irvine, they will fix it for a flat rate of $25, if they can not fix it they will replace it for free. They have a great customer support division, just have to get it down there. I would call first,
Irvine office
Shimano American Corp.
1 Holland
Irvine, CA 92618
On site customer support - Irvine office
8:00 a.m. to 4:30 p.m. Monday - Friday
Pacific Standard Time
Customer Service: 877-577-0600
6:00 a.m. to 5:00 p.m. Monday - Friday
Pacific Standard Time