I have polished cylinders like this with either a shotgun cleaning swab, homemade swab, and an electric drill. Polishing medium depends on the metal being polished. Chrome polish would probably work fine on the chamber. Coincidentally, I’m helping a guy work on the front brake of a motorcycle tonight that has slight corrosion in the master cylinder and this is what we will do. I’ve done it on several bikes with good results.
Thanks, I was thinking a short run with a brake cylinder hone might do it. What would you recommend for a final polish?