Have you tried any household cleaners like Simple Green, Formula 409, etc? If those spots are acid, the alkaline nature of the household cleaners might neutralize and dissolve them.

How about rubbing alcohol? Mineral spirits? Goo Gone or Goof Off? I'm thinking about things most people would have around the house to remove residues of some sort.

If none of those things work, you'll have to polish out the spots. This could be tricky in that the gauge lens is pretty soft plastic, so it might scratch real easy. But you could try something like Mothers Plastic Polish, Meguiars PlastX, or other similar plastic polishes. Use with a soft cloth and try to test on a small area to see about scratching.