Drmark12pa,
I use a HF 5 Ib tumbler for 48 hours for polishing small parts. Walnut medium shells and any suitable polish available. If vid endorses this HF tumbler then get your credit card out as you are good to go.
When I get your issue with pitting of dark marks I wire brush/ grind smooth. Takes a few minutes. I then re-plate using a cheap tin coating kit takes a further 30 mins. I then polish with a metal polish until it is gleaming. A spray of clear lacquer and it stays that way for a time. It the part is too big for my quart size re-plate container I do not re-plate but buff the dickens out of it. Probably a few hours.
Steve J