After sitting in heavy rain (this is the UK after all...) my car almost always has water sitting on the inner door seal in the same place, roughly adjacent to the front of the seat(s) – ie, about midway between the seat strengthener on the floor and the front 'corner' of the door opening. The door seals, both inner and outer, are all new from 914rubber. The consequence of this is that the water is absorbed by the sill carpet and then tracks down under the floor mat.

What I have discovered is that when you squeeze the seal, a fair amount of water is pushed out – the neoprene seal, instead of sealing against the door and physically preventing water getting by, appears to be soaking it up and allowing it to track into the car. Does anyone else have this problem? Or any observations? Having just had the rear floor repaired and a whole new carpet set installed, I'm keen to eliminate the leaks.

Was the original factory seal neoprene or rubber (sadly I threw the original away when I replaced the seals... doh!)?

I assumed it could be coming from the seal end around the door jam. Check the whole seal and probably the water went in and flows down the middle.

I have to admit, I did wonder about that. There are also little 'breather'; holes in the seal, out of which water can be squeezed. Maybe I'll try blocking the ends and the holes with some sealant...

OK, here we go! Found water had indeed got into the void inside the seal itself, presumably through an open end (even though the ends were tucked tightly against the adjoining seals). By blowing into the seal, it was possible to see how much water had collected inside and how it was coming out of the small holes left by the moulding process. Here's a video showing what I mean...

https://youtu.be/on-0yvOQv0M

The most obscure cause of water ingress I've found!

What you are looking at is the inner seal. It is not neoprene. The outer is and it will not absorb water. The inner foam rubber seal can. The OEM would have trapped even more in the crevasse the seal sits in.

These cars were never designed to be left out in heavy rain.

We have made some improvements where we can, but if the water has built up that much you need to rethink your storage options

It had actually only sat outside one night in the rain as it's normally garaged. Could the inner seal be made of something other than foam? Porsche or rather Karmann sure did make things difficult for themselves with the seals on the 914. :-)

As a co-extruded seal it could be solid rubber, but the problem is not this seal, The water should never reach it if parked. It has to be coming in from the end cap area or wiper seal. Check the other seals

I looked @ my seals and that's the only thing I could see would cause it,my seals don't have those holes in them .

The inner door seal helps keep water out mainly when the car is moving. It is also the 2nd barrier. It may hold water as it should. Ideally it holds water out but should work both ways.
The water is coming from above this seal somewhere.