Good thing you caught it (the brushes). How many miles on them?

I ask because my #1 daughter just paid $400 for an alternator plus whatever for the tow. Now she's going to hand the shop another $50 for the core so I can have a look at why the brushes I put in at 300K are worn at 350K, if that was indeed the failure mode. If nothing else, examining the core may tell me something about the local shop she used.

The feeling I get, is as these alts get older, the slip rings chew through brushes at a faster rate.

The insulator does just that, so you, looking closely, have the best idea whether it is still in good enough shape to do that job. Probably gets pretty warm down there under the manifold.
--
Art Benstein near Baltimore

Experience is something you don't get until just after you need it.