My method has been wiping then buffing plastics with lacquer thinner. Different plastics will react in different ways. Example - speedo cluster cover will 'melt' if treated with lacquer thinner in excess, but if wiped with carefully it will restore texture and gloss. There is a learning curve to achieve good results with it, surfaces can be easily damaged. But the inner fender or rear fender plastic type is tough and safe to use this method. After that, I use ArmorAll 'Tire Foam'. Spray, distribute with a finger all over the surfaces, leave for a few minutes while checking and spreading it evenly as it dries. Then a dry rag and buff it. It works very well on clear plastics like speedo cluster front cover window (don't use thinner on this!), fuse box cover, coolant tank, any plastic parts which are on electrical and electronic components. And the black and red rubbers on the starter solenoid and battery terminal. Rubber dust boots - voila! Tire foam will bring color and shine back to them.
