Hey, I've got an unidentified source of rust in my Honda. It’s located on the front doors at the bottom sills. The drainage channels are clear; I took apart the door and poured water over the window to check what would happen, but the water flows through the channels as it should. The mechanic told me it's not the seal, but I have my doubts.

Please pay attention to the seal ,as it has some rusty residue on it. Where does water come from ? Any idea ? Second door does not have this problem.
Do you have any idea what could be causing this? The car is a 2010 Civic Type S 3-door.