Driver footwell damp HELP!

[PugRory]

Footwell is damp on driver side, it leaves your fingers sticky and greasy and smells strange, can't see where it's coming from at all. It's on the rubber mat that's underneath the pedals and it's damp around it. Could well be the drains on the car blocked, I can see a few leaves in there but i'm hoping it's not the heater matrix as the whole dash comes out to change it! 

Any help is much appreciated