Hi all,
I'll apologize right off the bat for the length of this post...also if the majority feel the subject has been flogged to death in other similar posts.

My 2008 E70 (3.0d) first threw the old ABS/EBD/DSC/4x4 error at me in March this year and I went down a long road of hunting through the many posts relating to this error. Long story short I eventually replaced the ATC700 control module (the one that sits up against the body of the vehicle in the boot (trunk for you yanks) next to the battery. Problem solved. Please note, I did first remove and strip the transfer case servo motor just to be sure the gear was fine as it is after all the most common cause of this fault (Even though my diagnostic software explicitly noted "no communication" with the ATC700 module).

Last week the fault reappeared along with a long shopping list of others. I cleared them (I use BMWHAT for Android - a freakin' amazing piece of kit) and went directly home to try and figure out what went wrong. It was at this point I discovered roughly 2 liters of water in the left hand corner of the boot, directly below the HI-FI control module/amp. Also, there was damp in the matting which covers the fuse panel in the right hand side of the boot.
I removed and disassembled the fuse panel and dried it with a hairdrier. I had to clean the fuse contact board with electrical contact cleaner as well as scrape some caked corrosion from a few of the points which would indicated its not the first time this had happened. i also had to strip and clean/dry the HI-FI control module which was unfortunately very wet but somehow escaped damage...thus far. I completely expect some, if not all of the affected electronic hardware to fail down the line as a result of the bath they all took but am hoping my swift action may have bought some time. As for the ATC700 control module; while I know its not a sealed unit and water can very easily gain access through the rather generous seam around the edge, I really don't feel like drilling it open (I did with the last unit but found no visible evidence to suggest water had actually made it in, so have decided to let sleeping dogs lie.

Anyway, this brings me to the "why/how" in the story. Turns out there is a leak - obviously, but every single post I've found points to sunroof leaks...this is incorrect- or at least it was in my case. Pouring water onto the sunroof did replicate the leak, as did pouring water into the seams along either side of the car, however, what I found was that the water from the sunroof drained out of the two glands as it should (open the boot lid and look on the top sill, you'll notice two round black drainage points, one on the left and one on the right). The water from the "gutters" on the left and right hand side of the vehicle's roof also drained out onto the upper sill above the boot lid...and this is where we get to the problem. On either side of the sill there is a rubber boot which houses an electrical harness that passes from the vehicle body into the boot lid, for lighting and boot-lid lock I would assume. Unfortunately the water from both the sunroof and roof gutters flows directly over these rubber boots on both sides and in my case neither of the rubber boots were properly clipped into their sockets...the rubber boot above the fuse panel on my vehicle had been sealed with some type of rubber compound...ineffectually as it turns out but it would indicate someone (BMW dealer perhaps) has in the past attempted to repair this leak. Also of interest to some would be that when the vehicle is parked on an incline, the water accessing these two points flows into the rear light clusters as well.
I took pictures along the way but won't clutter an already cluttered post unless anyone thinks it may be of benefit to them in which case just pm me and I'll send them