I once tried to loosen the top lock nut on my starter's hot wire without
having a low profile wrench to hold the bottom lock nut. It didn't work,
the plastic part inside the starter that holds the bolt head wrung out
instead.
I took the starter apart. It has, like, springy fingers inside that hold the brushes.
Just be aware that stuff inside your starter will go SPROING when you take it
apart. It certainly can be put back together, but it would help if you had
three or four hands, and it would be good if some of them were pretty small

...
The plastic part I wrung out is about the only part inside the starter that
doesn't have a part number on the parts fiche... I found a low mileage
starter that looked nice (even if they work, a lot of salvage starters
are beater-looking) at pinwall... it was a pretty easy fix.
The starter is one of those parts that's really jambed into a tight place,
taking it off and putting it back on is annoying enough without
dealing with the SPROING...
-Mike