A water leak in that area could be coming in past the seal just to the rear of the wee black plastic triangle at the front of the window in the door. I think it is probably possible to silicone the seal to the metal although some silicones don't stick terribly well. If you remove the door trim (fairly simple if you have a Torx T25) you can pour water on the outside and see if drops appear on the inside. I think it might also involve a blockage of the channel by leaves and stuff, but i need to work out how to remove the outer black triangle to allow inspection of how it is put together.
Wee tip: I cut a slot in the rubber door seal at the bottom of the front curved section, cut from outside through to the groove, so that water drains away to the exterior. Do it both sides and it looks like a manufactured drain gap. Can also do at the rear if water getting in there, although I think my longstanding problem at the rear is actually coming in at the front and running rearwards when parked nose up. my car smells damp and i occasionalyy have to remove an orangey-brown fungus that grows on the surface of the carpet. If I can't get it fixed soon, the car is going.
