I had this exact problem and it turned out to be a bad seal on the heater box in the centre. My fix was to basically apply a whole bunch of silicon gasket maker around the seal and it hasn't leaked since.
To get to the offending part:
- Wipers off
- Take off the plastic panels that cover everything
- Take out the whole wiper motor assembly
- Once the wiper assembly it out you'll see the alarm speaker which is mounted on a bracket. The bracket is bolted through the duct in the middle so remove that. Once removed you should be able to pull away the duct from the blower.
Now when I did this, I seem to remember that I couldn't get the duct out from the passenger side of the car, even after removing the screen wash reservoir. The below is how I ultimately did it.
- Remove the panel behind the material that's on the bulkhead. Should be 3 or 4 10mm bolts
- The blower unit needs to come out. There's 2 bolts on the inside of the car. Poke your head up where the accelerator is and you'll see a black rectangle- this is the recirculation flap. There's 2 bolts at the bottom on either side that need to come out.
- You'll need to disconnect your AC lines from the part to the right of the driver strut tower. If you have AC (mine was all disconnected already so i didnt have to worry about this) there will be a lot of pressure in those lines so be careful.
- I also had to unbolt my intake manifold and move it forward a bit to allow enough room for the blower unit to come out.
- Once everything was unbolted the blower unit comes out and then you can also pull out the centre duct.
The duct seems to just use a foam gasket and mine was all torn apart and squashed which is why it leaked. I basically applied a ton of gasket maker to it and that's done the trick.
Do the steps in reverse to get everything back together. Again I'm sure I wasn't able to get the centre duct out from the right side of the car, avoiding taking out the blower unit. If it is possible to do it that way hopefully someone else can share some tips and tricks.
Hope this helps and good luck!