lots of degreaser and a synthetic brush will do the trick (swirling action). I drove 2 miles without a oil cap on a Mazda 323F (old school I know) made a horrible mess.
I did my with T cut paste, had horrible yellow stains on mine! apply...let it dry...polish off....repeat until clear. took about 30 mins. should of done a before and after.
Good luck, it will only be something small and silly. I always have my mechanic check the car other before he takes it down for the mot.
Fingers crossed it will just be washer fluid lol.
I'm in Watford area north m25 area 1st oct, with an Audi estate. My exhaust is on its way out and this seems ideal. If you don't sell it by then. I have the cash.
I very simply bought new number plates for mine this week. Normal font, no car sales numbers at the bottom, just plain Jane. But took about the space between the 55 and the next set of letters. Bit tatty anyway so looks much better.