Leak Under Rear Headliner

[gformica]

Hello,
I have a 1998 volvo s70 T5.
There is a leak that is coming from where the headliner meets the rear window, but only on the right corner.
Where the headliner board meets the right top corner of the rear window, a water leak has caused the headliner to come off off the roof and the water has caused damage to the headliner board in that corner.

Can this be a clogged sunroof drain?
Can this be a weather stripping issue?

Any thoughts would be greatly appreciated.
Thank you.