Sadly, when the brushes wear in the alternator, the slip rings tend to wear too. By the time the brushes need repalcing, the slip rings are often well worn too. They are much more difficult to replace. The connection from the rotor to the slip rings will present a sharp edge when the ring wears down, and this will chew the brush up very quickly.
By the time the brushes wear, the bearings will also be past their best. A complete alternator is a lot easier, and quicker to replace, avoiding the problem if rebuilding it. With aircon, the alternator is difficult to extract, so once out, you'd be wanting to refit and be done, not prolong the agony by rebuilding it.
I've not had a starter apart for years, but I'd expect the brushes to require soldering as they used to be. Again, there will be wear to the commutator segments, and the bearings, and the internal contacts of the solenoid. As with the alternator, I'd be happier replacing the whole thing, not attempting a short-term repair.