Same thing happened to my old Focus - basically water gets into the screw, corrodes the metal and fuses it to the base part.
You could try giving it a good turn with a pliers but I found out that it just destroys the rubber coating.
It'll be fine in the car wash though.
You could try giving it a good turn with a pliers but I found out that it just destroys the rubber coating.
It'll be fine in the car wash though.