I wouldn’t bother with trying to polish/buff a shaft that isn’t exhibiting undesirable symptoms (ie: leaking at gland), for mere aesthetic reasons.
Minor shaft scratches can be DIY hand polished, but deeper scoring or etching may require more sophisticated procedures (electropolishing).
Carefully* polish the shaft using “fine” wet/dry (300-500 grit silicon carbide) sandpaper or emery cloth working "radially" around the shaft. Afterward, wash the shaft thoroughly with fresh water
to remove any residual traces of abrasive, and apply a light coat of grease to ease reassembly.
* Any mechanically produced surface (ground, polished, buffed, lapped, honed, etc.) produces a work hardened, disturbed and damaged grain layer approximately 0.001" thick.