A ceiling stain, damp panel or soft spot near a vent calls for a moisture assessment. It does not tell you where it entered.
On an RV roof the entry point can sit well away from the visible damage, with water travelling along a seam, under the membrane or through the deck before it shows up indoors.
A useful evaluation looks at the whole roof surface, not just the wet patch: membrane condition, seams, and the sealant around vents, skylights, antennas and edge trim, plus the ceiling and framing underneath. Until that is done, choosing a specific sealant or patch is a guess.

