I have a SL R230 NIGHT EDITION 350 2010. Recently after taking the car through a SAINSBURYS car wash in the UK it opened the fuel cover and flicked it off. it has done this twice now. I now put some duck tape over the cap before the wash, if you forget then check after the wash to see if the flap is still OK. I was surprised that the flap just clipped back in place as the forks holding it could have been broken. This could apply to the R 231 and other models.

Captain Mike.