The Super Record post is anodized, and it may help to remove the anodizing with oven cleaner or some other caustic before polishing. That's what I've done on such parts that I wanted to "restore". The anodized layer is harder than base metal, so if your "polishing" reaches the boundary between anodizing and base, the results can look splotchy. I'm not going to get into what caustic to use, or how long to use it; you can look that up online.
By the way, that post looks to me to be on the border of "don't bother, too far gone". You may end up with a decent-looking post, but I don't think it will ever look great.