That ground wire is so far down under there that it might be easier to replace it while you have the alternator off for inspection or testing.

I usually take compressed air and blow out the windings as dirt does collect in there. The unit will run cooler and needs all the air flow it can get IMHO.

if you have it on the bench study the slip rings for a brassy/copperish look. You do not want to see any dark gray material or deep grooving or ridges that would keep the brushes from seating right a way.

If you go the rebuilt route check and see if the brushes they put in it have a copper impregnated finish to them. The copper ones conduct more current for the same contact surface area. Actually the good original Bosch brushes will have their symbol near the lead end on them.

If they look like the plain soft carbon type, they went the cheap route and I do not consider them as the best rebuilders.
I have seen Bosch rebuilds right out of the box, done cheaply. I have concluded that just because it says Bosch on the outside it does not mean they have total control of a rebuilders standards or the outlets they get sold too.

Good luck getting it back on line,
Phil