It's leaking though the plastic cover on the auto seat belt ramp, right?
I have the same problem. Heres my post about it in the online mechanic forum.
zerothread?id=149601
So far i've removed alot of the plastic covers on the leaking side and the weatherstripping. I noticed alot of gunk stuck in the water runoff spots in the area above the window. Therefore i think water gets trapped in there causing the water to leak slowly into the cabin.