Note in bottom pix, underneath the wiper motor, there is a black plastic panel going around the black circular brake servo. The servo goes into this black panel. Its the black panel that is sealed with black sealer round the edges and this cracks and causes leaks.

Pour water over this area and look inside the footwell and see if it runs in. Thats the best pix i can find online so i cant describe it any better than that im afraid.