Ah, okay.

The supercharger pulley bearing is a part within the supercharger pulley assembly. It’s readily replaceable, although seldom done by dealerships. They tend to replace the entire assembly.

Bearing replacement:
http://forums.mbworld.org/forums/sho...3&postcount=55

Bearing source:
http://shop.code3performance.com/pro...=3&productId=5

Good luck.