greaseball

when i first got my 88 toyota the alternator was working intermittantly. i took it out to clean it because it was caked with oil and grease took it apart and found the slip rings were worn half way through,cleaned them up and put new brushes in and it works like new. i tried to find a good used one at the wrecking yard but they were all missing,must be a defect or new ones are too expensive i wonder what caused the slip rings to wear so much i read of a website that sold the slip rings cheap i was wondering if anyone else knew of one or should i upgrade to a higher amprage gm alternator.