I have been working on a 200s one piece rear fender for two days now.
It was so badly oxidized the thing was light pink. I actually started with 80 grit and worked through 120, 220, 280 and now I'm on 320 on my way to 400, 600, 1000 then 2000.
One thing I have found once I reached 320 is water is as much my enemy as my friend. There's a balance. Too much water and my paper (3m wet/dry) will stop cutting and sweat equity is lost to oblivion. Too little water and and the paper loads up, scratches and you start over. Everyone's mileage will vary but I have found instead of recreating Noah's flood like i did with 80 grit where I set the hose to a trickle and left it dribbling over the fender while i worked, a soaked cloth to keep things wet and CONSTANTLY checking your paper for build up works best (for me). About 15-20 strokes, wipe, rinse paper and repeat.
By the way, polishing plastic SUCKS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!
I was born and raised on Venus & I may be here a while.....