RetrObrite is something that folks use.
Here is the link to it:
http://retr0bright.wikispaces.com/
I ripped this off the Airstream Forum:
http://www.airforums.com/forums/f39/...tic-50799.html
Hi all. Pretty much all of the plastic in our 1976 Sovereign was very yellow and I really didn't want to paint it if at all possible. Thanks to the wonders of the Internet we came across this site RetrObrite: Open Source Problem Solving - PSFK.com
We figured if it worked for computer plastic it should work for the plastic in our trailer so we gave it a try with excellent results. The concoction is cheap and easy to make with ingredients found at your local drug store and beauty supply. The instructions are available on the website but I would be happy to post the recipe and instructions here. You simply make up the gel, brush it on the plastic and put it out in the sun.
(Pictures on the original post)
The first shows an untreated piece in the lower left corner then clockwise a piece treated one time and two pieces treated twice. Once it is back to the original color it won't lighten any more. The second picture shows a piece that was treated except for the back that won't be seen. Some of the mixture dripped down and illustrates how well it works.
We did all of our plastic including the large pieces in the bathroom and I am amazed at how great they look. Yay no painting!
This was another post:
Hydrogen peroxide is a chemical that can cause burns to the skin and can cause blindness if splashed in the eyes so please wear gloves and eye protection when handling it. The following recipe has been tested and is safe to use when prepared properly. If you decide to deviate from the recipe I don't know what might happen.
The recipe for the gel I used is:
8oz Hydrogen Peroxide 10 to 15% (I used 40 volume from Sally Beauty. Make sure it is a clear peroxide and not a creme. You want as few additives as possible)
1 1/2 tablespoons of Arrowroot powder (This is for thickening it into a gel. Cornstarch might work just as well.)
1 teaspoon of Glycerine Oil (available at a pharmacy)
1/4 teaspoon of an Oxy-type laundry booster powder
1 teaspoon of hot water (to dissolve the oxy powder before mixing it in)
gloves (grabbed a box while at Sally Beauty)
small paintbrush
eye protection
In a glass bowl or plastic container mix the peroxide, arrowroot and glycerine oil. Microwave the mixture for 30 seconds and stir. Microwave another 30 seconds and stir. Let it sit for just a bit and stir it again. The mixture should begin to thicken and may be sufficiently gelled at this point. If it still seems too watery microwave for another 15-20 seconds. It won't smell very good but it doesn't produce nasty vapors or anything. Let the mixture cool for a bit while you dissolve the oxy powder in a bit of hot water. The gel will not activate until the booster powder is mixed in. Once the dissolved powder is mixed in your gel will foam up a bit. The warmer the gel the more it will foam so make sure it isn't super hot. I used a metal whisk to mix it in really well. Grab your brush and coat all areas you want brightened with a fairly good layer of the gel. Put your pieces in the sun and leave them there for several hours. I left mine all day. Rinse off the gel and reapply if needed.
Doubling this recipe in an 8 cup glass measuring bowl coated all of our plastic pieces one time. Make sure all of your plastic is clean and dry before you start. I have found that three applications got mine back to the original color but YMMV. We haven't applied any sort of plastic protectant at this point but if anyone has any thoughts on this please let me know.