The plastics on my Yamaha Kodiak ATV were faded and oxidized. I searched the web and a 60/40 paint thinner to boiled linseed oil mix seemed to get good reviews. I saw some before and after pictures using this method, and I thought it was too good to be true. Well, I gave it a try, and the results were nothing less than spectacular. See for yourself.
If you try it, please leave a post and let me know if it works as well for you as it did for me.
UPDATE June 3, 2013: The ATV still looks great. The oxidation has not returned and the red is still bright!