I think using the same heat that caused the fading in excess is just going to cause even more damage, especially when exposed to UV again.
On my plastics I've had the best results with straight-up DOT 5 brake fluid. Not the DOT 3 or 4, or DOT 5.1. These will eat the paint. But DOT 5 is made of silicone, and it soaks into faded plastics like nothing I've seen before. I use a cotton gardening glove and just wipe it all over, with some on a q-tip for the crevices. Lasts through many rain storms.
I dribbled some on the plastics and blacked-out engine on a Harley while servicing the brakes. Knowing the stuff was not going to eat the paint, I left the spill there overnight and when I wiped it off, I was amazed at how it had refreshed the blacked out engine paint and all the plastic and rubber bits it had touched.
I think it's loads better than the overpriced S100 stuff. Lasts a whole lot longer and way cheaper too.