Bubble Scrubbles, Scrubbing Bubbles or something like that cleans it up good.
Not much uv protectant int it and it is white. You can buy the stuff by the foot and pop the old out and new in.
The various little plastic pieces on RV will all do that and eventually the hard stuff will crack an fall apart.
There are two or three or more plastic paints that work well on cleaned and white hard trim to protect it.
The new automotive paints will outlast the rest of the RV. Perhaps a air brush gun and small amount with elasticerzes or whatever mixed in on the hard stuff.