Hi all, I know this is a very old thread (last reply I saw was 2019) and I couldn’t find anyone posting a confirmed fix, so I’m adding this in case it helps someone in the future. I had this problem myself this year on my 2006 Fabia Mk1. I was getting water under the carpet and I also found water inside the A-pillar itself, not directly from the door. In my case it was the passenger side, but on UK cars this will likely be the driver’s side. After checking all the usual things like door seals, speaker membrane, grommets, etc., the real source turned out to be the door check strap (door stop). The metal arm of the door check goes into the A-pillar and is held with two Torx bolts. Around its base there is a rubber seal/gasket where it sits against the pillar. On mine that rubber was not sealing properly. I should also mention that Breezy_Pete had actually pointed to this area in an older post, but at the time I couldn’t believe water could come through there because it has a rubber seal. Turns out he was right. I saw it with my own eyes: water was running down the pillar, collecting around that opening and forming a small “pool”, and then the water in that little pool suddenly disappeared as it got pulled inside through that point. During heavy or continuous rain (I could never reproduce it with a hose), water running down from the roof and windscreen area flows down the A-pillar and directly over the door check area. Once enough builds up around that opening, it enters the A-pillar, which then fills up and eventually overflows into the cabin and under the carpet. That’s why the door interior was dry, the seals looked fine, and the leak only showed up in heavy rain, with water appearing inside the pillar. I removed the door check strap, applied sealant/silicone all around the base where it contacts the pillar, then refitted and tightened it properly. Since doing this, after a full day of rain, the pillar is completely dry and no more water under the carpet. It’s a very hidden leak point and easy to miss because it’s not a typical seal area. Hope this helps someone finally solve this issue.