The key is when you sand it, to have the right grit paper and feather the paint.. If they are just faded, and not flaking, take a red scotch bright pad to them and then mist the paint on in several layers.. last coat for evenness of sheen. If there is flaking, sand them with 80 to feather the paint, and then step up to 150, then 320. Then coat 2-3 times, and if you don't like how they look, let them dry and then sand them with the 320 or 400 again and repaint. This will fill the scratches.
If you use a penetrating oil to remove the wipers, make sure you completely wash them off. Paint won't stick to the stuff, and you will be sanding it into the metal if you don't get it off. Which mean pain will never stick. Use it as a last resort.