If the bearing is worn out, or out of alignment inside of the case (which means that it's worn out), the slip rings are probably not far behind. So, you could either buy a rebuilt alternator, or take your's out of the car and take it to shop that an auto electrical shop and have it rebuilt. This will cost far less and the shops often rebuild the entire alternator. I've paid a premium for rebuilt Bosch alternators in the past only to have them fail hard (bearings, slip rings) after 18-24 months. Took the factory alternator to an electrical shop after the Bosch replacement failed, and the factory alternator is still going 6 years later.