I had a similar situation on my '86 last spring and the alternator needed a rebuild. ask around and you will find that there is probably a place in your city that can do a rebuild for @$175 with new bushes and a VR. While you have it out, you might as well just rebuild the whole thing.
Also, if you have been intermittently killing your battery, you may want to put a fresh one in after the rebuild. My failing alternator killed the battery which in turn stressed the fresh altenator to the poiint of needing another rebuild.