Hi Cameron
Would you believe that I have the same issue with my passenger door. And I am looking for a solution. I own a MY 2006 C70, and after heavy rain when the door was opened water poured out of the door and the sill was wet, like you, the car interior is dry. On investigation I found that a small square hole had been made in the bottom of the door at the opening end. This was obviously something done by a previous owner. It turns out that water was gaining entry to the door via a gap between the window glass and the seal. What I don't know is how to correct it. So I am hoping some of the more experienced members will be able to help. I think it will require something to be adjusted, but I'm not sure what, or how to solve. Most definitely help & advice is needed.
Fred