i'd Try to service the starter. they are as solid as a brick. those metal blocks are carbon brushes, they are supposed to conduct electricity from the static parts to the spinny parts. they wear out over time, so they are springloaded with hairclip springs which press them onto the copper (the commutator). under the grime you will see that the commutator has many segments, with isolator in between. as the rotor spins, the brushes touch the various segments, which generate the magnetic field in the rotor, which have the rotor spinning in the first place. its basically a 'rotary switch'.
your stator looks so grimy because all the carbon dust from the brushes. if you look closely you'll find leads attached to the carbon brushes. one of the connectors is isolated, one goes to bare metal. undo them, then you can remove the springs and slide out the brushes. clean the brushes with something non-oily, like brake cleaner or isoproyl acohol. the rest of the armature (the part that holds your brushes) you can soak in fuel or ultrasonic and clean it with a old tooth brush.
the bushings (at least my Honda CB250G Starter had bushings) on both ends of the case are made from Oilite, a porous brass which can wick up oil. you can remove them with the ominous 'bread trick', or heat up the case and shake them out, but mostly, reoiling is good enough.
The stator coils can be removed as well, but i'd try not to. its a hassle getting it back together again. try cleaning with brake clean, and maybe scotchbrite the anchors (metal inserts around which the copper coils are wound), then dust off.
on the business end of the starter there is a planetary gear (at least there was one on my starter). and a paper gasket which most likely will tear if you open that end (which you want to do if you want to remove the rotor). clean and regrease with fresh grease.
the commutator will have wear marks, from the constant friction of the brushes, and will have black carbon embedded in the copper. Clean the surface with scotchbrite to a nice shiny copper color. ideally, chuck the rotor into a lathe and skim off the commutator, but scotchbriting will get you far. clean the rotor anchors as well (rotor and stator move very closely to each other, any rust or dirt inside the casing can cause the rotor to bind up).
replace the carbon brushes with new ones, or reuse the old ones if they are still 1/2 inch or longer. make sure they slide up and down freely (if you ever watched a youtube-'will-it-run?'-video where the car DIDNT start and the youtuber hits the starter with the hammer, he does so to wiggle the stuck brushes free...)
reassemble in reverse order... now you have a starter that will last you another 50 years...
some visual support for the task at hand:
