We just got the first hard rain on our 2014 37FS and ended up with a soaking wet spot right under the bunk slide. I remembered reading this post earlier and, sure enough, I had the exact same problem.
The bottom trim on my bunk slide was pulled away a good 1/16" on one side and, as a test, I poured a little water in the gap and it quickly started dripping off of the trim screws in the bottom. During the rain storm I had the slides in and the motorhome was not leveled so the water just flowed along the bottom of the slide right into the motorhome instead of dripping off of the screws.
The problem looks like it was caused when Jayco installed the sealant too far out on the bottom trim. The factory butyl putty was installed outside (relative to the corner of the trim) of the screw holes. If the putty was installed on the inside corner of the screw holes or even over the top of the screw holes there would be no leak.
We are a long way from a dealer so I decided I would tackle this repair myself.
I don't really like the exposed screws that Jayco used in the post above so I decided to use a little butyl putty along the top seam of the trim to keep the rain from ever even getting behind that trim. To make room for the putty I just removed all of the screws along the bottom side of the trim and slowly and gently pulled the trim out enough to make room for the butyl (1/4"-3/8").
I stuffed as much in there as I could get in the crack and let the sun soften it enough that I could push the trim back in place and run the screws back in the original holes. The screws kept pressure on the trim and the rest of the day the butyl oozed out of the crack until the trim pulled up tight against the side. What a mess- but I know the seam will be completely sealed now. I started off using some masking tape to help with cleanup but abandoned the idea after a while. I wish I would have left it there because getting the butyl off the side of the motorhome is a lot of work. If I do the other side I will try the masking tape idea again.
Anyway... I still have some cleanup left to do but it is looking better already and no leaks anymore!! Total time spent was roughly 2 hours (not including the ongoing cleanup to make the seam meet the wife's quality control standards
I hope this helps someone searching for this problem later on like it did for me. I would have never found the problem without this post.