I'm glad I took the advice of those on this forum to have my alternator rebuilt by a professional shop. At 144,000 miles on my '88 Carrera, the alternator bearings were making that dry "rustling" sound and so this Spring, when the garage was warm enough to work in, I removed it. Took it to a local auto electrical rebuilder and got it back in 7 days.
This is the 90 Amp Paris-Rhone alternator which is common on my vintage Porsche. I instructed the shop to go through it thoroughly, clean, replace bearings with non-Chinese - made parts, and replace anything suspicious. They found quite a bit of parts that were worn out.
The slip-rings were severely worn (actually worn through in one spot) and these were replaced:
The brushes are non-replaceable as separate parts and the whole brush holder and regulator is replaced as an assembly. Brushes were right at the end of their travel:
New bearings are Japanese-made NTN brand, which are very high quality.
I feel that this alternator was severely worn out and caught in the nick of time. Thus, my recommendation is for others with 3.2 L engines with 100,000 miles, you might want to have your alternator serviced.
Getting caught up on maintenance items now that the coronavirus has me housebound. Since most Spring PCA events are cancelled, it's a good time for a detailed and extended maintenance program.