Is your clear plastic yellowed or scratched? If it is not, wait for a better reply. If it is I would gently try to scrape it off. Then using a sanding paper (depending on scratches, yellowing or cloudiness) use anywhere from a 400 grit max (your particular problem would dictate what grit to start with) up to a 12,000 grit sand paper (Micro-mesh kit for plastic refinishing can be found on-line) and with a little elbow grease you should end up with a pristine finish.
