Starter rebuild

Went to spin the bike over after a starter clutch replacement and just got a click. On a hunch I pulled the starter motor and tried to spin it over by hand and it seemed bound up. Opened it up and here is what I found:

I'm not sure what the black powder is from but the brushes seem OK and there do not appear to be any broken parts. I'm wondering if I should just clean out all the dirt/powder and try it again. If so, can I use regular solvent or do I need some kind of electrical solvent?
If I decide to replace I remember hearing there is an upgraded starter you can use from a Honda? This is for the '82 GPZ750.

I would guess that the black powder is carbon dust from the brushes. I'd be carefeful with using any kind of liquid as it could turn into a mess. Maybe experiment with a bit of brake cleaner ?

You could try a shop vac or compressed air and a toothbrush

On further thought be careful with any solvent as it might remove the covering on copper windings

I agree with JR. It's probably dust from brushes. Not too long ago, I rebuilt my starter and found tons of that black stuff all over everywhere. I just used electrical parts cleaner and that seemed to work