i bought an old stainless shelf a while back, it was rusty and oxidized… i just took a few of those green scratch pads and “barkeepers friend” and cleaned the crap out of it… got about 95% off.
Now I also have an old aluminum attachment for a Hobart mixed… it’s extremely oxidized. I had to call Hobart about it, they told me to get a liquid cleaner, can’t remember the name of it though, and use it… should take all the oxidation off. I never got a chance to do it though.