Its called a seal guard. To put it on you have to unbolt your top shock mount, and under the long bolt that passes through the frame, swingarm and motor. After that the swingarm should come right out. Remove the old seal guard, put a new one on and then just re assemble it.
they also make aftermarket ones that dont spin and the chain just rides on them. i bought one and it works awsome. all i did was cut that one off with dykes and bolt the new one in place
Hey guys, the tech at the dealership pointed to this and said "you could use a new one". Problem is, I have no idea what it is called. It's the little white plastic roller thingy. :-/