I had a small scratch in the door panel from my ring. I could just catch it with a fingernail so I knew it would not come out with any "easy" method such as Meguire's Plastic Polish.

I used the same method I would use on a light scratch in the clearcoat. Started with a 2000 grit wet sandpaper (lightly), moved on to a rubbing compound, then a polishing compound, then a "paint cleaner" or "light swirl remover", then a coat of wax. Looks flawless now. Took around 45 minutes.

For really deep scratches, you may need to start with a more aggressive wet sandpaper (1000 or 1500 grit) before moving on to the 2000 grit.

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2005 X5 4.4 (Sterling on Truffle) w/sport everything
2011 Audi S4 (Prestige, DSG)
2012 Audi Q7 (Sport, S-Line)