That's a pretty neat trick- - - -making a "generator" from a starter! If it was working OK before you disassembled it, don't worry about the deterioration of the insulation. If it makes you feel better, use an air gun to blow away any loose stuff and mix up some 2 part epoxy cement to recoat that area of the armature. Don't increase the diameter enough that it will drag on the housing. You should change the brushes and bushings while you've got it apart.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!