Had something very similar in my old S2 Elise, water was coming in around the rubber that fits around the window for the mirror, quite strange, never got it fixed though so no help really but I think that maybe your problem as well.
Tanman
Are those original doorcards? Maybe the plastic sheet has been disturbed when they were fitted? If you take the card off it should be easy to see if the seal is tight at the top.
Mine had a leak from the area adj the mirror, the dealer fixed it after i moaned. Also it somtimes leaks in the the rear bottom corner of the drivers door window and either spits at me while driving or if parked it can run down the seal to a similar position to yours and then down the door card. I would let the dealer sort it, if now then go round each area in turn with silicon grease. At least that way you can narrow it down.