I get brushes from the dealer, they are considered expensive. But I consider if $20 of brushes, a new front bearing and a few hours to go through it makes it last, that works for me.

To get more power from it requires rewinding it. I have an electric motor rebuilder that can do it, He rewinds armatures all week long. Some starter and alternator shops my still know how to rewind. Most just cleanup a core and send it out.
I have not had it done I have not rewound an armature since the slot car days.

I did just mounted a 110 amp unit from a DOHC G72 onto my SR engine in place of the 90 amp.
If you have a 75 amp or less the 90 amp is the same case size. There are two different mid size housings, 3 bolt or 4 bolt. You can swap the front case to adapt an alternator to different engines.