I'm sorry ladies, but I happen to agree with the fella from the other forum.
I use toothpaste to polish out hairline scratches and scuffs on the plastic "crystal" on my Rolex. Works great.
I have also used Meguiars Cleaner Paste Wax too with an everyday household rag. Works great too.
The watch is 40 years old and the original glass crystal had a crack in it so I had to replace it. Rolex does not make retro glass crystals for my model - it changed over time. However, they make a plastic knock off that looks identical except that it scratches. I had it serviced by Rolex in New York City. (AWESOME office by the way!)
If you have some lightly scratched plastic lying around and you can experiment on it, then try it!