A quick DIY tip for severely scratched car windows.
When I bought the 500SL it had scratches on the passenger window, most of which were concentrated in a half inch swathe from top to bottom. 23 years of there being some trapped grit in the rubber seal had done it's work. Looked all over the internet for advice on how to remove them and found the only solution was jewelers' rouge. Made up a block using beeswax and powdered rouge and gave it a go, but it took several days using a buffer on a drill and an orbital sander, and even then it merely rounded them off a bit and didn't eliminate them completely.
I finally bought a 2nd hand window from eBay, which had been described as VGC, but on receipt it proved to have similar scratches in the same place and was therefore unusable. I managed to get a full refund and was told to keep it. Given I now had a spare window I thought I'd try an experiment and attacked the spare in the same manner you'd approach car paint - i.e. with some wet and dry.
Used 1200 grade wet and dry till the scratches were completely flatted out (but the glass was now frosted) and then used 1500 grade wet and dry to reduce the opaqueness. Finally buffed it with the jeweler's rouge. Perfect result. Took me no more than a couple of hours of hard work.
Tried the same approach on the in situ car window with the same result. Bingo!