Hi all I recently refitted the inside of my van over the past few weeks new rear internal panels, re-carpeted and new floor speakers,lights etc as you do, and a rear reversing sensor unit. The van was untouched over the Christmas period and had not moved, then about a week ago I received my new side window trim so decided to go out and fit it, So I started the van to move it forward tad away from the garage, and to make sure the battery was all ok, when I put it into reverse the sensor was on a permanent noise as if it was up against a wall so I never thought anything straight away, I contacted the people I got the reverse sensor unit off and they sent me out a new unit (AFTER A BIT OF ARGUING AND TELLING THEM, WELL THE VAN HASN'T MOVED). So yesterday I decided to refit the new unit, I started to take off my near side rear internal panel as the sensor unit is located just in front of the rear light cluster, as I put my hand in to try to reach the unit it was Pi$$ wet through...as was the insulation. I found the leak to be like a large grommet about 10cm wide which is located just behind the side door slide panel which in turn is held in place by 2 star screws one near the rear light and one near the in-side of the van where the door opens when you take of the slide cover panel you can pop out the grommet, and I found that the foam ring had perished so I got out the old bathroom sealer and resealed the grommet and then put everything back including my new sensor unit, and it all works fine now. I just thought I would warn others as it would never have been found unless the sensor unit had been fitted there and the inside of my van would have probably rotted from the inside. for the sake of taking off the two external screws it may prove worth it..