If you're not familiar with it (not to insult your intelligence) that's a boot and the purpose of it is to keep the rack clean. I would say take it to the dealer so they can inspect it for any issues and to clean it incase any rocks or dirt got onto the rack. If you can't do that then make sure it's clean and lubridated then get a new clamp and just clamp it back down. A screw style hose clamp looks like it would do the trick. How's the steering? Any unusual noises?