Question for the Honda wizards, if starter runs with direct power after taking nuts off, wouldn't the starter just need new terminal nuts for a better connection, and not a full rebuild (internals/brushes etc etc)?
I'm no wizard but I think I can answer your question. The reason the starter runs temporarily by disturbing the positive post is because the positive brush is either worn too short to maintain constant spring pressure contact with the commutator bars, or that brush is stuck in its brush holder (caused by corrosion buildup on the holder), preventing the brush from contacting the commutator bars.
The positive post has its brush lead spot welded onto the bottom of it on the square section of the stud. By disturbing the position of that post the brush lead may cause the brush itself to shift inside its brush holder a bit, make contact with the commutator and run momentarily.
Once the brushes are worn too short to maintain constant commutator contact at a specified minimum pressure (see the FSM for the minimum brush length spec) heavy arcing begins to occur on the copper commutator bars and destroys them quickly. But... if those worn out brushes are replaced before any commutator damage occurs the starter motor may provide a 2nd complete life cycle of service.
The commutator bars may last for several decades (brushes are engineered to be sacrificial, the commutator is not) provided those brushes are maintained in good condition. So its beneficial to the owner to take their starter motors apart periodically for inspection and replace worn parts as necessary.
Now about that tip I mentioned earlier... the brushes are made from a mixture of soft, conductive metals and contain a high percentage of graphite. Graphite is a useful conductive solid lubricant as you all know... the high graphite content in the brush metals lubricates the commutator bars. A thin layer of graphite is deposited on those bars over time which serves to minimize arcing on the moving surfaces as well, by filling tiny voids, scratches and imperfections on the surfaces left from the machining operations. That buildup may become glossy smooth and is very slippery, highly conductive and protective of the soft copper commutator bars.
SO, for as long as the commutator remains undamaged from any heavy arcing caused by worn/stuck brushes, leave that thin layer of graphite alone. Do not polish it off of there. Doing so introduces a new wear cycle and shortens the service life of the motor.
A bit long-winded ehh? :-)