Metal polish and 00 grade wire wool. If that doesn't shift it then move up a grade then back down. It will take a lot of elbow grease, so be prepared for arm ache. You can get drill attachments but I've never gone down that route.
A Huge +1 from me on the 0000 wire wool and Autosol polish.....a little hard work and you will prevail.
Personally, I include them ALWAYS as part of my wash routine, it only adds a few seconds and soooo worth it.
Mine are nothing special, just standard but still look like new after 6 years and 102k miles, as below