One last thing to try that won't hurt the finish even if it doesn't work. Take a clean soft absorbent cotton towel or a micro polishing cloth. Make sure there is no dirt or residue on the cloth. Put a dab of baby oil, (or any light oil like you would use to lube the blades of an electric razor) onto the cloth. In a pinch, vegetable oil might work too. Rub the stain in a circular fashion until it is lifted. Be careful to have just a thin coat of oil and not get it anywhere but on the stain. After the stain is gone, you can remove the oil residue with a solution of water mixed with a bit of isopropyl alcohol, or monitor cleaning wipes.
I have used this method to remove a lot of tough stains. It works by penetrating the substance so that it can no longer stick to the surface it's bonded to.
If this doesn't work, I think you have scratched the surface and the stain is embedded in the substrate.