After 18 months of driving my 1990 Mazda Miata, "GRACIE", I found the plastic lenses to have been damaged by sandblasting from the beach, road salts and sand, and dirt road crud from the road my Mother lives on (Starvation Road - REALLY!!).
I decided to see if I could remedy the problem, since I can't afford to buy replacements. It worked out much better and much more simply than I thought possible.

1. Remove the lens you wish to work on, using a Phillips #1 screwdriver. I recommend doing a set at a time, rear markers, front markers, taillights, or parking lights. Make sure you know which position each light came from, marking it if possible.
2. Using a good quality Mill Bastard 6" file, remove the raised lettering from the lens. Don't get in a hurry, you want a smooth surface with no gouges.
3. Use a 4" x 4" piece of 320 grit wet & dry sandpaper under running water to completly blend in all of the surface of the lens. This grit works fast, it should only be a short time till your'e done (5 min. for marker lenses, 15 for taillights). Check your work by drying with a clean cloth, and seeing if the surface has a uniform finish. If not, go at it again!
4. Use a piece of 4" x 4" 400 grit wet & dry sandpaper and repeat Step #3.
5. Use a piece of 600 grit wet & dry and repeat step #3 again!
6. Using a clean terry towel, put a dollop of "Nu Finish" car polish on one corner. Apply in a cicular motion, working it into the lens surface, using light pressure. If you feel a smooth and constant resistance, your'e probably done. Using another corner of the towel, wipe and clean the lens off.
7. Reinstall the lens, step back, and admire your work!!

I did all 8 lenses on my car in about 3 hours, but that included learning how to do it! The longer you use the finer grits of paper, the better your results. Don't let the surface of the lens get dry, the plastic is soft and can gouge. You can tell when the paper is done when the resistance to sanding becomes less. Checking for uniform finish will keep you from having to repeat a step.

Just remember to be cautious on your first try till you get the hang of it! An added bonus is that you won't have that unsightly and annoying wax buildup in the lettering of your lenses, and you just won't believe how much brighter your lights can be!! This method will work on any plastic lens, including the M2 Headlight.