Had a leak on a Fiesta once it only happened if left
out in the rain never a drop being driven only when
parked, what was happening the water was some how
coming up over the rear of the front passenger door
sill if you looked you could just see a fine line of water
going down the inside of the sill and onto the carpet
it looked for all the world like a very fine trail left by
a slug and it did not wet the carpet that was on the
sill it's self only the floor quite strange really,
but the carpet was wet through it was amazing how
it got over the sill and how much was getting in, just
gave the door seals a clean and it was right after.
I don't know if this helps but it proved to me that water
can flow up hill.