I had the same issue with my FW 24F - floor was wet with the slide in. Here is a video of what I found. I have since sealed everything as well as shifted the bottom trim about 1/2 inch towards the main coach to create a weep drain. Tell-talel for me was the discoloration on the inside wall of the slide.
https://drive.google.com/open?id=1Yl...btb6u_2Vf6TqZm