RadTech sells several kinds of Ice-Creme, some just do the plastic, and others do heavily scratched plastic and metal. I've been meaning to get some for a while. I would recommend something like this before even considering using Brasso (which works well on dirty tuning slides )
No matter what cleaner you use, whether Ice Creme (quality) or Brasso (cheap) or whatever, I suggest that you polish with a microfiber soft cloth to get the stuff off. I recommend an iKlear cloth. Kind of expensive, but worth it.
I've tried Ice-Cream from Radtech. It's really not very good. It'll get rid of those hairline stratches but anything beyond that and you'll be polishing for the best part of 2 hours trying to get a noticable difference.