The clay bar is what I'd use first, too. If the car has its original paint, there's no clear coat, and likely not a lot of paint either, if it's been cut & polished a few times over the years. If that doesn't work, try some 3M Finesse-It polish. If you need to use 3000 or 2000 grit sandpaper on it, use plenty of water with a few drops of dish detergent added.