W124, rear seatbelt shoulder opening water leak

[wolf_walker]

I'm assuming this is a sunroof drain clogged or otherwise malfunctioning, had our first really hard rain and the boy-child says "um, there's water here" lol..
Sure enough, leak after sitting but not while driving from the pass rear seatbelt shoulder belt opening in the C pillar cover. Known issue by chance?

[Zulfiqar]

most probably a sunroof drain is stopped up.