THe original thread appears to be read only, I can't respond to it but I have some info for the poster. Last year our S40 had the same thing happen. It turned out that all of the drains were completely clogged up, so water was pooling in areas such as below the windshield and then seeping down over the firewall under the carpet. First, you have to pull out the seats and center console and get the carpet out to dry because the water is under the rubber backing and it will never dry in situ.

While it's drying, clear out all the drains: remove the trim under the wipers and clear out that trough and drains, the drains in the front fenders in front of the driver and passenger doors, and if it has a sunroof the sunroof drains. The best way is if you have compressed air to blow it all out, but a shopvac would probably work too. We also used a coathanger to poke through the sunroof drains. In fact the first rain we though it was just the sunroof, we put the carpet back in and it rained again and soaked the car again! So we've had to dry the carpet twice but I sprayed it front and back with lysol and then let it dry for 2 days, the lysol prevented mildew from growing and the car smells like new again.

In our case the car we bought had been parked under trees a lot - we found oak leaves in ever nook and cranny or the car including inside all layers of the cabin filter, in the passenger compartment! The leaves had been left for so long they had decayed and formed a gunky soil that stopped up all the drains.

Good luck I hope this solves your problem! OUrs has not leaked since :)