Well, not sure if I have mentioned this before, but after years of playing around with Retrobrite formulas I have found the perfect version (for me anywayz)... Napisan Gold Gel (bright pink bottle)...... that's it!
It has an oxy agent etc all ready in it, it is a think pink translucent gel which does not dry out in the sun. It is perfect. You simply open the bottle, pour some in a container and then paint in on your plastic with a brush. Done.
It does not cause any blooming or bleaching, it does not dry out (in 40 degree heat I only have to reapply every couple of hours and after a couple of applications it is usually done anywayz) and requires no mixing etc.
You can find it at any supermarket. Hope this helps.