I didn't know about water leaks in the 159, but couldn't understand why it kept steaming up. From previous experience over many cars and year, suspected wet carpets, and more specifically, wet under-carpet sound deadening. A root around revealed way more water under the carpet in the 159 than I'd ever found in any other car ever. I suspected leaking floor bungs.
Search on here revealed the inner door panel seal issue - so dried the car, by removing the front seats, and lifting carpets and wedging them up, mopping up the water, squeezing as much out of the sound insulation (that i was surprised to find part of the carpet - but pleasantly surprised to find each front footwell section was a separate piece - I'd attacked other cars with knives to get bits of carpet out to dry), then leaving it shut up with a dehumidifier in. Resealed the inner door panels with dum-dum strip, rather than silicon - I wanted to be able to get them off if needed in the future.
Tried again. Was fine for a while - no steaming up, but kept checking under the carpets (under the front seats where there's a gap for the wiring loom). Found water again, so seats, carpets out, and start looking. Found water in the A-pillar. Sealed everything into the A-pillar - had the front wing off as much as possible to seal screw holes, and thing that looked like a gap. Sealed the rubber bungs and check strap cover with hylomar. Shone bright lights in from the outide, and out from the inside, with the car in a dark garage. Sealed the loom bungs through the bulkhed - one of them hadn't quite been installed right on assembly, the sealing flange was't quie through, but I don't think it had leaked. Checked all the drain rubber boots.
Supsected the seam that has been mentioned - certinly seemed to be allowing water into the A-pillar - do dried it and sealed it. At one point I had the drivers side of the bonnet off it's hinge and the hinge out to seal it's mounting holes.
Applied watering cans of water and lad upside down in the footwell, looking up behind the dash - finally found a drip in a seam behind some insulation wedged up above the accelerator pedal - which from under the bonnet is an overlapping seam under the trim panel under the screen. I didn't want to seal inside the car when I could see it, as that would simply trap water in the seam - and I didn't know how long I would be keeping the car - but seeing as I've had an integrale 20 odd years, the Caterham 15yr, the Pug similar, probably a while, and I didn't want to be repairing difficult to get to rust in the future. So blew it dry with compressed air, left it inside the garage to dry properly, and finally sealed under the screen on the seam.
So far, despite torrential rain, snow, hail, it seems to he working. I never did seem to be able to stop all the water getting in the A-pillar, but there are drain holes in the bottom of it that drain into the sill - and drains immediately under that to the outside. So I compromised on giving it a good misting of Noxudol 700 inside. As there's way less water running inside, it doesn't drip out inside the car.