Ive just had this issue with the wifes Laguna II.
Passenger carpet was soaking wet.
After drying the carpet out with our Bissell cleaner, i set about investigating....
Took me about 45 mins, but i realised the door deal was not fitted correctly. At some point the windscreen had been replaced, and the front windscreen rubber was on top of the door rubber.
I did a comparrision with my car to make sure this was the case.
So using a small screwdriver, i pulled the door seal out so it was not trapped under the windscreen rubber.
Also i noticed the small channel in the door seal on her car was heavily filled with Algee. This was preventing water flow and drainage. So i cleaned all the door seals on the whole car.
Finished with a 15min test using the garden hose and success !!. No more leaks.