Spanner, as odd as this may sound, toothpaste could be your answer. Wet down the try out area first, then rub on your toothpaste with a dampened rag, then rub off with a clean dry cloth - my old singlets work a real treat here. Try it on a not so obvious area first.
Another idea is to go to a large used car yard and seek out their detailer. The car yards have the same problem with older headlights; their detailers have ways and means of bringing headlights back to original brilliance. (Not all headlights are glass)
Otherwise open Youtube and type in your problem. You'll be surprised at what you'll find.
Or you could try your local Repco, or Supercheap Auto store. They usually have kits that will do the job.
Cheers,
Peter
