Cankin,
As suggested above, I would simply glue it back for a quick fix.
Another solution would be to take your cans back to your original dealer. Show them the issue and have them remove and order you a replacement metal gimbal assembly with height rod under warranty. The gimbal assembly is available for order to authorized Grado dealers only.
If the shop does not feel comfortable removing the gimbal assembly and suggest you send in your cans for warranty. You can either ship them directly back to Grado Labs or to the Audio Group, the Canadian Grado distributor for warranty service.
Best,
Kev