Hi,
You will probably find that the leak is coming from the bolts that hold the passenger front seat down!! the two back bolts of the passenger front seat are situated exposed, underneath the car.
You can buy new bolts and seals for this from Renault or do a diy job with some flexible rubber sealant, which is what I did and had no more problems. I didn't even touch any seals to do with the door!!!
Good luck!
Clyde - Southport - Merseyside, May 2006