I use Birchwood Casey Aluminium Black to touch-up tiny spots of worn anodising on scope turrets and other areas.

Scope mount ring marks on the tube will often polish out with Brasso Duraglit Wadding, but it will make a matt finish more satin, so you need to polish the entire tube to keep the anodised finish even. A couple of tips, polish lightly and avoid polishing any painted-on numbering or lettering, as the wadding may remove it!