Okay, im writing this because i just had lots of glue tip on my windscreen and after having a nervous breakdown i recalled something the dude at the local hobbyshop said :P
He said he dropped his car and something happened and it scratched the shit out of his clear parts. He then mentioned that he sanded it down and used toothpaste to fix it up.
Well, anyway. This doesn't have any pictures because its a simple thing to do!
Please be warned: this will not COMPLETELY fix up the window, but make it pretty darn close to perfect
1. Use a high grit sanding paper (i used 2000 and thats why theres still some scratches visible) and sand down the area that needs work. This works perfectly if you accidentaly cut the clear part with a modelling knife. Completely sand down the area, but be careful. Casually increase the grit # until the scratch is no longer visible.
2. Now the clear part will look FUBAR, don't worry, it won't stay like this forever! Use a polishing cloth (i used one that scratched my car, so maybe thats why my attempt still carries a few imperfections), and either use compound or toothpaste (toothpaste is a mild abbrasive so it will cut!). Lightly rub the compound into the clear part that needs the fixing. Once the first layer is done, wipe it off completely and repeat the rubbing part until satisfied.
3. Lastly, wash the part quickly in some tap water. The area should be clear now! If result isnt as desired, repeat from 1.
Be warned however, i strongly suggest you try this on a spare or broken piece of clear part before! I thought it wasn't too bad a mistake for my car, so I went along with it, but if you want a perfectly see through-without-scratches windscreen, i suggest you order that particular tree again.
I hope this helps some people who are upset over a big scratch and think it cannot be fixed.
See ya later!