Lincoln Repair Questions? Ask a Mechanic for Answers ASAP
Pop the trunk and look for water in there. No, I don't think it's water from either the ac drain or the heater, but just a simple question why would you be using both ac and the heater? Anyhow, I think the water is still there after cleaning it up and driving and hitting the brakes makes it slosh around and if it's in the trunk when you hit the brakes it is making it through to the rear drivers floor. It's worth a look.
Ok, check the trunk again on the passenger side of the trunk if there is a spot that dips way down, like where the quarter panel is, usually on most cars they can fill up with water.
Other than that, I honestly have no idea where the water is coming from.
I have one more suggestion although I don't know what could possibly be under there and that is remove the rear Footwell Duct. I see the procedure in the climate control section but honestly I don't know why it is there so it might be beneficial to at last look under it and see if there is water in it.
Here are the instructions for removing it,
And if you decide to do it, the instructions for removing the front seat.
ok, I don't know what else to say.
Did you find any water under that footwell duct?