I just replaced the slip rings and brushes in my alternator. It started dropping in voltage then dropped to zero. It works great now. Grease and dirt fouled up the slip rings, one was worn almost completely down. Cost me about $40 in parts and tools (battery terminal puller, to get the bearing off to remove the slip ring assembly). I was planning to do a write-up on it.

2000 Mitsubishi Montero Endeavor, "Katsumi", 138k
1993 Toyota Tercel, backup vehicle, 93k
1989 Isuzu Trooper, "Beniko", R.I.P. at 233k

My 'Genuine Isuzu Parts' decals - for sale