Danny,
I've heard toothpaste will work on scratched plastic...even on Cd's.
Not sure about clear plastic, but it does work very well on plastic keys.
You can do a Google search on what type to use etc...
I hope this helps.
Ian
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Yamaha Tyros4, Yamaha MS-60S Powered Monitors(2), Yamaha CS-01, Yamaha TQ-5, Yamaha PSR-S775.