Citroen C4 Cactus bodywork help

[S2r]

I have a problem with our C4 Cactus, more specifically marks in the 'air bumps' all around the car that I can't seem to remove. They have been 'growing' for a while, so not something that's happened in the past week or so.



So far I've tried washing it, various degreasers, contaminate removal spray, even a squirt WD40 but nothing seems to even reduce the staining - the picture above is after trying all of the above. As the panels are slightly textured and soft plastic I don't want to use anything abrasive;

I did wonder if it had some sort of clear top coat on and it is water / dirt under that, a bit like when water gets under the lacquer on diamond cut wheels.

Any ideas what else I can try?

[threadlock]

Bleach? Looks like it could be mould