Car goes in for an MOT on Tuesday

so I spent the last few days making sure that it's not going to fail on anything obvious. One thing I noticed was that the rear fog light wasn't working. Must be a bulb? Not that easy.....Someone has put the rear fog light on incorrectly and the drain holes were at the top

so water was getting in. The bulb was corroded into the fitting

FFS what fool did that? Anyway it is all working now but I had to turn the light and the fitting round the proper way so now there is overspray on top of the black fitting. Never tried to get overspray off what's the best way? Paint stripper water down or is there something else? (i'll take the rear fog off the car again)
Cheers,
BMCC