[Dark Skies]

Sounds like you're going through the same problem I am currently suffering (see soggy carpets about a page back). Assuming that it's not attributable to the battery box leak the 944 is oft afflicted by...

Sounds like a sunroof leak (which is what I've had) Either the little drain holes are blocked or the internal pipes have come adrift. If it's not either then it could be a weeping sunroof seal or, as mine is, water creeping under the plastic trim in the roof hatch. Often the leak cannot be seen because it sneaks past the trim and then drains down the back of the speaker panel, down past the seat and onto the floor near the seat belt fastening.

If it's the latter it takes a lot of effort to dry all that foam and sound deadener out.

Could also be where someone has pushed the sunroof button by accident after the ignition switch has been turned off - rendering the sunroof removeable and less water tight.