Great thread this, lots of good information
I drove out in my 8 on Tuesday night and heard a "sloshing" noise but wasn't sure where it was coming from. Music off, drove some more, decided it was from above rather than below me. I decided to have a look at the weekend as time after work is limited, as is daylight right now.
Drove out last night and first right turn saw copious amounts of water cascade from the headlining near the C pillar and drench the seat
This prompted me to take a look tonight as a matter of urgency and armed with the information provided here I cleared and cleaned the sunroof drains, both of which were blocked. The area had a build-up of sediment so I assume this gets washed down the drainage tubes and blocks over time. It took some effort to force some plastic tubing down both sides but once down there I could flush both sides with hot soapy water, then flushed with plenty of cold water to follow. The drivers side blockage was more difficult to shift so I improvised by pushing the tubing down as far as it would go then attaching a stand pump and introducing pressure very slowly until the blockage cleared. I felt this preferable to attaching my compressor and bursting the pipe, as Del suggested might happen
Scuttle panels removed afterwards and cleaned and flushed so hopefully I've caught this before any real damage is done. I really can't emphasise enough the views of others that these need to be cleaned regularly, I feel like I've had a lucky escape this week.