The Two Separate "Copper Looking" rings on the Shaft of the Alternator,
That the Brushes "Ride" on making contact.(Slip Rings are all one Part)
If they are worn Too much (You can catch a Fingernail in Them, USUALLY
means REPLACE.)
That's what's Chewing up your Brushes.
Thing is they have to be Soldered in with "95/5" silver solder and then
"Trued Up" on a Lathe.
If everything ELSE is G.T.G. (GOOD TO GO) an Alternator Shop should be
able to install and True your new Slip Rings.
Get the BOSCH part Number off your Alternator (It's on the Black Plastic Back Cover)
And call these guys about a new set of S.R. s
http://www.wagneralt.com/
(909)465-1950