stumpjumper

see if you can find Novus 1-2-3 and use step the middle step and last step, it'll clean up very well... but unfortunately if you ever use the most abrasive it develops swirls that show up in sunlight... so if the sun is behind you it's tough to see through (I did this unfortunately) the middle and last step work great though

or go to a marine store and buy plastics cleaner, it doesn't have the polishing steps that Novus has but is essentially the same as the last step

you can also find stuff called Plexus which is similar to the last step of Novus

lilredpo

I've used both the Meguiar's plastic cleaner and polish (no 17 and no. 10) on boat and car windows with success. Keeps them in nice shape.

Although, applied only only by hand.

I've read posts that recommend to use a machine or even wetsand. Has anyone tried a polisher?

http://www.autogeek.net/meguiars1017.html

Silver Box

If it is just opaque and not torn or cracked, I would definitely give the plastic polish a try first. I had really good sucess with Meguiars Mirror Glaze Professional 17 Clear Plastic Cleaner. Take your time, concentrate on a small area, don't apply too much pressure - let the cleaner do the work, repeat 2-3 times if it's still cloudy but you're starting to see results and do both inside and outside.