What does this plastic part do?

[benhogan]

On the W126 front passenger footwell. If you remove the floormat, there is a black rainbow shaped vent looking duct.

Does anyone know what it is for? I suspect rainwater is getting into the car via that duct.

Is it possibly the source of my water leak?

I have cleaned the sunroof drains. However, water still gets in somehow. It only gets wet in the rear passenger footwell very close to the driveshaft hump under the front seat.

Any ideas are more than welcome. I would like to remove the plastic duct to double check. Thank you very much in advance!