when they get like that you should see if you can find someone with a armature tester
i dont rebuild them when they get that bad anymore without testing them as they tend
to have some bad windings and will work well when cold but then wont crank over properly once the engine
and starter get hot they wil crank over slowly so if its a customer bike i just put on new as with labour to clean the stater
and a brush kit ts cheaper for the customer to just to open the box and put new
so if you need and bits for your i have a pile of them
good luck