Leaking sunroof

I have a 1980 300D wagon with manual sunroof and every time I wash my mb and sit in it I see water streaking down from above now I belive there is a drain pipe which is supposed to prevent that from happening. Does anyone has any idea where exactly that pipe is so I could flush it.
My rear windscreen defrost also does not work the switch lights up upon selection the fuse is good no obvious damage to windscreen checked visually .
Any suggestion will be greatly appreciated thanks