Wet rear seats coming from a leak which looks to be coming in through the boot and then under the seat?

OMG! Thank you for your help! I had been experiencing a water leak in the backseat of my 04 Golf where the seat back meets the bottom. Bizarre! No window leak. No door leak. Where was the water coming from? I read your article and yesterday finally got to investigate. I checked under all carpeted areas and in the wheel well. Nothing. Hmmm. I decided to take apart my “trunk” area as well. Nothing still. I thought why not and removed my spare tire and there it was! The missing grommet that was letting the water in from the road and NW Oregon is wet!! I fixed the hole with a rubber plug and silicone. Thank you for your help!! Now I can put my back seat back together. I was afraid of mold. In the 2nd photo you can see where the water had been pooling and the related rust.

Inside the rear wheel well behind the plastic liner there should be a rubber grommet which is used to access different wire harnesses for different equipment. Ex. all wheel drive, HID option with leveling sensor. The grommet might have come loose or is missing and probably has a small tear which let rain water from the road enter your vehicle. Also underneath the rear seat is the fuel tank which has an access port to service wet fuel pump assemblies in the tank. The cover plate must be off it's rest position and letting road water in when it rains.