Low voltage problem
I went through 3 rebuilt alternators before I got one that worked. Good luck!
OP has a local rebuilder.
That is pathetic to have to go through 3 rebuilt alternators.
Maybe a good plan is to have any alt we purchase tested by the store selling it before we leave the store.
I had no issues with the last rebuilt I bought except it was advertised as a round back and came in as a square back wired for the 1 field wire VR.
I had them send it back and get another one but it was a square back too.
I called the rebuilder directly (US based rebuilder) and they said the round back cores are non existent.
I went ahead and put the square back on till I found a round back. Worked fine but it had the almost 3" pulley so idle charging was not good.
The replacement round back had the 2.5 pulley and idle charging was back to expected.
It sounds like the OP has the know how to check and replace the brushes, and a reliable rebuilder nearby.