Dirty Looking Arches

Quite a keen detailer, however the one thing that annoys me every time I clean my 197 is the fact the arches still look dull and dirty.

I normally snow foam the car and get up inside the arches, rinse and then use APC and brushes to agitate.

Apply Aerospace 303 when I clean the arches with the wheels off. The plastic however just doesn't seem to take to it. . .

Any suggestions/ideas. I'll post some photos up when I get chance next.
 
we use silocone spray on our 200s keeps them looking fresh for a long time, spray on to a cloth the rub in, i have had no problems of spatter etc as it would be highly noticeable on the raider
 
Halfords own make is cheap and does the trick. Just spray it on and wile off. Use it for engine bays, carbon bike frames and all sorts.
 
I find crap just sticks to that. Silicone spray makes it harder for crud to stick to the arches and keeps them shiny