leak from sunroof

[geeceed]

my 300e has a leak which I believe comes from the sunroof drainage line, it only leaks in heavy rain and never whilst travelling. the leak appears on the trim at the top of the door and then drips onto floor........ My question ,how do you replace the drainage line..... I was thinking of trying to put a tube down the old one and hopefully block off the rusted section to try and stop the leak. The leak is at the passenger side front. Any suggestion will be gratefully recieved.