Just putting this out there.
Been chasing a leak in my slides. After hours of taping and testing I found the leaks. To check yours just remove a few screws from underneath the outer T strip of the slide wall. If you have rust on them more than likely you have the same problem. The water can get to the wood in the slide bottom. When running the slide in and out it flexes the T strip back and forth breaking the seal on the outside wall. I tested the leak by taping the outside joint and spraying with a water hose. I sealed all 3 of my slides and replaced all the screws with self tapping screws into the metal strip underneath the slide. The self tapping screws made the T strip more solid and less likely to flex.
Glad you caught it. Very common spot for the sealant to crack and leak, rotting out the entire slide floor before its caught. It is commonly referred at the "Picture Frame molding"
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Brian & Jeannie
2018.5 Seneca 37RB with to many mods to list
2015 Jeep JKU Rubicon