[Restyle]

Quote:

it might be attributed to the fact that i've been running the aircon on very hot recently

I think the AC removes a certain amount of moisture from the circulated air so its unlikely to be that ..
But .. Might be an idea to see if it still does it when you dont use the aircon.
{Personally cant see the point of using AC in the winter, & only used it a couple of times last summer, although people say its best to switch it on at least once a month to prevent things like airlocks in the system}

Quote:

...seems it happened since BMW replaced one of the metal sills.

The Door step sills? ... If so then I`d be closely looking at the door seal in that area, & might be an idea to get someone to spray a waterhose around that area whilst your in the car. If even a drop enters, then thats the problem.