Plastics: Many people think that the best way to fix plastic is to squirt some Krylon on thick and call it good. This is the worst thing you can do to restore plastic. The first thing to do is scrub all the oxidized plastic off. I use a power sander with 120 grit paper. Sand it until there is no fading left. Don't panic about the scratches. Once all the fading is gone switch to a grade #00 steel wool. Scrub the scuffs out, and yes this will take some muscle and time. Now change to #0000 steel wool. 
Once again a lot of time and muscle. Concentrate on the corners and crevices and make sure they are clean. At this point the plastic should be clean and almost shiny, but still a little dull. The final step is to apply either an Acrylic finish (easy!) or a clear resin finish (more difficult).
Once again a lot of time and muscle. Concentrate on the corners and crevices and make sure they are clean. At this point the plastic should be clean and almost shiny, but still a little dull. The final step is to apply either an Acrylic finish (easy!) or a clear resin finish (more difficult). 
To apply an Acrylic finish simply get under the sink and pull out a bottle of floor finish like Future. Verify all the dust if off the plastics and then rinse them off. Take a new sponge and dampen it. Spray the Acrylic floor polish on to the sponge and apply an even coat onto the plastics. I simply pull the the sponge evenly the full length of the fender. Acrylic dries very fast so don't try to touch up anything. Simply apply another coat in twenty minutes. Don't apply more than a coat or two or you will get some flaking. If you do have a paint gun and some clear coat you can really spray a thin coat that will last a very long time.
