Our Cooper S had a somewhat serious leak into the boot area where the tools would be kept. I have an aversion to any dealership so we found a local company so that we "could talk to" the actual people doing the job. The water was coming in at the centre of the lid on the shelf above the channel that carries the wire harness from the left tail light to the other side. There is a gap between the tail light and the trunk lid and the water was travelling along the channel above the harness wires and then into the trunk via the area where the pressure relief flaps are located. It should run out directly but wasn't. They resealed all plugs etc and then installed a plexi-glass "dam" inside the wall where the pressure relief opening is. It is just in front of the tin/aluminum plate that you can see through the opening for the pressure relief flaps.(Pry off the cover) They had to take off the external bumper plastic covers to get at the area. We can now see the water draining down and out of the car. We pressure tested it and washed the car and it seems to be ok now. Time will tell.