We have a similar leak in out '96 (front passenger foot well) but not on the driver's side, yet. Also larger leak on both sides at the back. I haven't been able to figure out where the water is entering. An experienced indie shop here in Vancouver told us to park in a garage...
Two different glass shops were amazed that our factory windshield wasn't a replacement because it doesn't really fit very well - the rubber covering doesn't fully cover the top edge of the windshield (where it meets the roof there's a gap almost big enough to stick your finger in) at all. Still, it is really just trim. The experienced "Broco glass" manager said to replace the windshield and see if that helps. I won't do that unless the glass gets broken however... too dear.
I have the impression (not properly tested) that the water gets in quickest when the vehicle is parked at a slant with the nose slightly up.
Apologies, all this isn't much help. Don't forget, this is a Brit vehicle!
PS: To get at the water easily, I removed the thick spongy mat in the back and folded back the carpet, likewise in the front where I keep a piece of wood to elevate the carpet. The Mrs. sponges out the water after every heavy rain. Finally, in the channel running along the edge of the floor under the rear door, there's a plastic plug in the middle.... remove that and the water can get out.