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Some older cars just don't have the right lacquer/UV protection, so they will always fade. You can delay the fade with wax and ceramic coating to add UV protection but it will always fade, like the Volvo has. Neil I think planned on having it resprayed if he'd have kept it, which I intended to do as well, but now is not the right time financially. The respray would add the right clear coat to stop it fading in the future. Obviously the problem with repeated machine polishing is the paint depth will get lower and lower until there's no red paint left.
I owned a Tornado Red Corrado G60 that had turned several shades of Tornado Pink as old VW's do. I remember one cleaning session buffing the panels for hours and it was gleaming. The panels were hot to the touch and my dad had gone a bit over the top and buffed through the paint on the swage lines. It looked great for the afternoon and had started to fade again by the next morning.