I love in the Netherlands and have the same issue. Having water inside as well. But I think that it came from the AC drain pipe. Because it appeared in the summer when there wasn't any rain at all. Don't know where to find this pipe. But only the right side is getting wet. ( drive the LHD vesion) carpet is wet. Styrofoam underneath is wet.
Got some days of between Christmas and new year. Will search for it then.
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