I use this stuff on headlights. My buddy turned me on to it several years ago when he brought it home from work (aircraft mechanic). They use it on aircraft windows so I know it will work on your lexan windows. It might take some time wet sanding with this stuff, but I promise you by the time you get to 12000 grit it will be perfectly clear and like new.
Ive also used it to polish stainless steel and aluminum and it does an amazing job. Basically a very fine grit sandpaper.