i've got that one too.. the water pools on top of the lap vent and when i turn a corner my ankle gets soaked (@#$%!). i have narrowed mine down to either a firewall plug, or the door/window seal, mine are pretty weak! could also be your windshield seal. mine was leaking there til we put a new windshield in it.
My 79 is leaking somewhere about 8 inches back from the A pillar. It is either water wicking up through the screws that hold the window molding track in place OR there is a crack in the roof rain gutter.
You basically have to gut the drivers side interior and outside moldings to locate exactly where the water is coming from. It is not a pretty job.
I get a shower when I turn left and break.
The bad side of all this, is that with all the interior pieces in place, the water will end up running down the A pillar and onto the ECU before it hits the floor.
It is very easy to break the plastic molding when you remove them, after 20 + years they are very brittle.
Use a garden hose and put water into the air vent in front of the windshield, that is another place these things like to leak. There must be a drain in there somewhere but I have not found it yet.
Leaves and dirt can get into the molding behind / over the rain gutter and plug them up also.