Once again, my apologies for the belated response to your replies.
Thanks for the tips - I'll give it a go next time I have the top fairing off. I really don't know how they got messed up - it's not scratches, just sort of stains. Must have been something pretty caustic. They actually just look like regular water stains, but obviously not.
Thinking about it, I'll try putting them in my ultrasonic cleaner with some Sea Green.