Water dripping from headliner - 2000 e320 wagon
 

We had quite a bit of rain yesterday, and while driving in it I noticed I was getting a slow drip out of the rear passenger handle that's attached ceiling just above the door.

Someone suggested that maybe a drain tube that is supposed to drain water from the sunroof is plugged.

Has anyone seen a problem like this before? Any suggestions on what to do? I'm not sure where to start looking for the clog if that's what it is.

Thanks,
Pete