Roof Leak!

[zlilz]

Two months ago, I noticed the roof headlining was wet on the rear left passenger side. It was right at the edge where the headlining met the trim. It started about half way and it got more wet further back. I took the roof headlining off and noticed the 3 inch drain tubes on the left side was getting old, so I replaced them on the left and the right passenger side.

Two days ago, I noticed the rear right passenger side was wet. Not moist like previously, but dripping wet. I took the headlining off again, but I couldn't see where the water was coming from. It has been off since and there is still no sign of water leakage.

Does anyone have any ideas? The front of the car is fine. No water, it's just the back