You can polish the slide as it is stainless steel, but the receiver is anodized aluminum. Polishing the receiver will result in the removal of the anodizing, the anodizing provides corrosion protection and surface hardness. Although it can be done, and some have done it, I don't recommend polishing away the anodized finish.
Nothing further?
I have tried MOTHERS and I don't have the patience to do it by hand...I'm not confident to use any power tools on it myself.