Had same issue 2015 Vegas. Replaced all seals to start with and final fix being sure when slide out all seals lined up properly at top where they meet
You need to check inside as much as possible and outside
I have small telescoping camera I use a lot to get in dark corners
Trial and error on this fix
You could b holding water in that awning that usually extends when out
Takes some time to go thru steps and use water hose to check what is going on
My issue started after 3 in driving rain and took couple trips to repair shop to finally get seals right
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