As with (occasionally) most of the W211s and W212s I've had, the front parking sensors on the E63 seem to be a bit prone to playing up after heavy rain due to water ingress. I've seen somebody suggest that WD40 is a short-term solution. I presume I just wait until there have been a few dry warm days to be sure they have dried out completely, then give them a good squirt in situ, without any dismantling, and wipe off the excess?