use wet and dry papers after the sandpaper , plenty of water, up to 1600 gritt if you can find it or the highest one you can find , you will probably find it will have a grey-ish /white colour when your done , polish this out with plastic polish compound , like t cut but for plastics , do it all by hand , using a drill or sander to speed things up can generate to much heat in the plastic and cause it to ripple. you can get specialist sizal cutting mops for plastics, for use in power/air tools that don't cause the heat problem and give the best results, not cheap to buy though .
