Hey this is Vatriker, I have a tip for yall.  

How to make chalky faded Yamaha (and others) yellow fenders look new. I do not know about the other yamaha colors, but this does NOT work well for honda red. I also recomend that you try this for yourself in a small hidden spot if you are going to do it. 
  
#1 If the plastic is badly chalked and faded: first take a razor blade and stand it on edge (NEVER CUT INTO IT) then drag it across the plastic. This will scrape the heavy chalk off. 
#2 I use napa 60/40 paint reducer, but others may work. Drench a wad of VERY fine #00 steel wool with the paint reducer and scour the plastic with it frequently re-drenching the wool. You will work up a kind of grey slime --wipe it off with a rag. After you have done this until the plastic is clean and without any chalking or fade left you can go on to the next step..PS you can remove paint on fenders this way too.
#3 MAKE SURE THE PLASTIC IS SPOTLESS! NO DIRT. NO SCUM. IT NEEDS TO BE CLEAN. To do this, drench a clean rag with the thinner and wipe plastic down to get the grey scum resudue off. Now wash with dish soap and a clean rag. LET IT DRY NOW. 
#4 Heat gun ( this is why it needs to be so clean) TAKE YOUR TIME DON'T RUSH!. Heat the plastic with the gun (if plastic starts to change color GET HEAT OFF IN A HURRY!). Try to only melt or soften a VERY thin layer . While plactic is still hot spray Son of a Gun vinyl protector on it. If it produces steam when you spray it on then you did it perfect. LET IT COOL. Then you can wipe the left over spray off.
 
I HIGHLY RECCOMEND that you practice on the bottom or in a hidden spot before doing the entire thing. This is tried and true: I did my YTM 200E this way and it looks very nice now, but I practiced on several scrap pieces first.  

Have fun, 
Vatriker