One of my early projects was to run the slide out, then inspect & correct all the seals. There was several spots that water could have flowed in, but with some simple mods and sealant here and there, all has been corrected.
If you can see light with a fully retracted slide, you should examine the areas & make corrections if possible. Else, run it back to your dealer & demand it be fixed.
Formerly: 2000 Four Winds 26Q/Ford, '96 Kit Sportsmaster 22' 5th wheel, '91 Sunlite truck camper, Wildernest flip-top canopy