Have you checked the elephant trunk, if it gets blocked it can back up and start leaking into the footwell from what i understand. I noticed mine was the same on the passenger side, took of the elephant trunk and it's full of crap.
Positioned just behind the engine on the bulkhead, you should see a black bit of rubber hanging down. Pull it off and see what it's like inside, give it a clean and pop it back on, easy 5 min job.