Go to www.langka.com -- they've got some advice, and their product works. For scratches, you MUST degrease thoroughly and let the touch-up paint dry 24-hours. One trick with Langka is to use a thin piece of cloth (bedsheet) on the plastic card, or it will pull the paint back out of the scratch. By the way, I found a very similar product at the local auto parts: Mother's makes something "with Langka technology" at $9.95 a bottle instead of $19.95 a bottle. Seems a little thicker than the Langka stuff -- both work.