It seems like there is an issue with 2CV's and water getting inside the car,generally?
Well, my car is 100% waterproof and I do not think much about it cus I kind of expect it to be. When I bought it I did a lot of work on it before I even began to use it. Chassis, floor, went-flap, brakes and lot's of small things. I could see traces of water on the dash, so this is what I did:

Dismounted the wiper-axles and checked it. Not very worn, so I greased them up and mounted then back on. Changed the went-flap under he windscreen. New flap and seal, Made sure the "bend" on it was the right way and mounted it, using nothing but the new rubber seal, taking care it got mounted like it is supposed to. The went flap is totally watertight now three years later, without any grease,duck(?)tape or sealant. Just the original design with the rubber hinge/gasket. The car had no leaking the first year. Then last year it started to leak, and I took out the windscreen and repaired the rust under the window-seal and applied new tape over the openings in the A-pillars under the windscreen-seal. Then it was 100% "waterproof" again. This year I've been driving in all sorts of weather, and there is not even moist on the floors. Or the boot for that matter, even with a boot extension. If water starts getting in again, I think the bonnet hinge is next to receive attention, cause there are some rust.

In my opinion there is not a need for anything than the original stuff being in good nick to keep the water out. If water is getting in, there is something wrong!

By the way, I tried 2CVikings tip of using the rubber dustcover of an old breakecylinder over the wiper-axle on a car of a friend. Worked great, and is a solution if you don't want to do the job properly with new grease/parts.

This is my contribution to the problem

hmm, because on one side my vent, you can see the light even when its wound down shut, and on the other side you cant see the light but it leaks

what do you suggest?

Haha wtf?!

no chance!!

I loosened the vent flap nuts, applied some masking tape along the paintwork just above the rubber seal and injected black silicone between the rubber seal and the body. Tightened the nuts, removed excess silicone and then removed the masking tape to give a clean line. That seems to have fixed the problem.

The other solution with all of my 2CVs is to drill two holes (about 6mm) on either side of the front floor, close to the foot board. There is a cross between two channels that is ideal. This means that any water that does leak in also leaks out.

When you have 6 weeks accumulation of red, powdered bull dust (after a Raid in Australia), and then leave the car out during a very heavy rainstorm, it is disconcerting to have to clean a car full of red mud. For the Raid car, I may add two 3/4" holes plugged with rubber grommets so i can hose the inside clean in future.

But the concept of a waterproof duck beggars belief.

Daffy Duck

I've never really worried about it. They leak, my knees get damp ... well, I was wet when I was born and it did me no harm. I see the 2CV as a bit like a faired motorbike: it'll keep the worst of the weather off but not all of it.

well i had a motor bike for a year, and after sliding round corners in january in the pi$$ing rain and on icey roads (never fell off just would loose the back end every corner) i'm grateful for a roof over my head!