it's very hard work to polish metal that's scratched, especially the thin stuff....my advice is dont bother............spray the case instead.
because to get rid of scratches you have to rub it down with Wet and Dry first, polish will not remove scratches...a scratch is too deep...even a fine scratch..you'll always see it after polishing!
bare Aluminium/ Stainless Steel is so easy to scratch...... you only have to look at it and it scratches, the inside of my new Lian case is fine, but the HDD tray that i luckily don't need...is scratched to hell........... it's been scuffed on something.
mind you, everything scratches doesn't it.............even a 1/2 million quid Rolls Royce.