I just wanted to say a big thank you to all on this thread, I have a 730d F01 and found my windows steaming up when parked in the sun, I also noticed the sound of water sloshing around the car, checked the rear passenger carpet and it was completely soaked. Did an online search and came across this thread.
I thought I would tackle the task this last Sunday, now I am completely useless at mechanics and would never have dreamed of doing the fix myself if it was not for the clear instructions on this thread. I managed to get in from the top after removing the big plastic cover on the engine, when I removed the cover there was lots of foliage at the bottom of the compartment, the grommet was black not yellow until I gave it a good clean. I put everything back together, two of the screws were a bit tight so I thought I would put some WD40 on them before inserting them, on the last screw, just as I was about to tighten it with my hand it slipped and fell onto the pan cover at the bottom NO!!!!!!!!!!!!! I thought. This sort of thing always happens to me.
Anyway, to cut a long story short, I managed to use a magnet to pick up the screw and fitted it back, have tried to soak up as much water as possible without ripping up the carpets, the car is currently in my garage with the windows down which should help it dry out. I will see if this has sorted out the issue.
Once again, a BIG thank you to you all!!