If the leak is between the siding and window frame, you'll need to remove the window, clean up the frame and siding, and reseat it with fresh butyl tape. These windows are removed by removing the inner trim ring and then removing them from the wall. After reinstallation, use a bead of self-leveling Dicor sealant on the top side (see your other window and door openings for reference) to keep the water out.
If the leak is between the rubber seal and the glass or frame, you might see what a glass shop would recommend for a temporary or permanent fix. If it were me, I might try some clear silicone sealant (generally not recommended for most RV applications) as an emergency fix simply because it will bond to damp surfaces.
2016 Ram Longhorn 3500 Dually 4x4 CCLB, 385/900 Cummins, Aisin AS69RC, 4.10
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