E39 Wagon - Sunroof Leak?

[BoneStock]

Any advice or assistance...I have leak in passenger side backseat floor. The carpet is wet and the rubber floor mat has water on top. No visible signs of leaks from sunroof or other interior components of car. My mechanic looked at it and blew out the tubes...seems like an improvement but after a heavy rain it is wet again. Any ideas? I posted exploded parts diagrams below...do you think replacing tubes would fix and what is approximate cost? Do it yourself? I see water repair kit in other diagram? Any advice or assistance would be appreciated?

[Speedster56]

I also have a leak causing the rear passenger floor to be wet after a rain storm I first thought it was a sunroof drain problem. However, some things I noticed suggested it may be a rear door seal. After a rain, the step plate under the door held quite a bit of water so that when the door was opened, it would splash on the driveway. Second, I noticed that the same result, wet carpet, occurred when the car was parked on a flat driveway or when the front end was higher than the rear. I turned the car around for a storm so the front end was lower than the rear and I found the carpet was completely dry.
My conclusion is that the rear door seal has compressed causing a water leak to buildup under the door to the point where it leaks under the inside trim onto the rear foot well. It only happens on the passenger side.
Haven't replaced the seal yet and I may try further testing to see if I can isolate it further.
Hope this helps.

[BoneStock]

Thank you, Speedster. My mechanic fixed it quickly. The water was coming from the heater vents under the passenger seat. Something was clogged in the engine compartment? Air cabin air filters were replaced just over 6 months ago? I have not had time to speak with him about repair.