Rubber boot, little thingy of grease. You really should take off the axels and get the grease in there before putting on new boots. I did this on my old CRX once, no biggie. Mine went at 60K.

NHTSA's defect report shows that the Passat's heat shield may not be long enough to guard the car's right half-shaft grease boot. As a result, the boot may leak grease, and if that grease comes in ...