The first thing to do is figure out whether the leak is really coming from the vent flange, the sealant around it, or a crack in the vent itself. A lot of RV roof leaks that look like “vent leaks” are actually caused by failed sealant, loose screws, or a damaged vent cap. Get up on the roof safely, clean the area, and look closely for gaps, lifted edges, dried-out caulk, or places where the sealant has pulled away from the plastic vent frame or the roof surface.
If the old sealant is just dirty but still bonded well, you may be able to clean it and apply a compatible sealant over it. But if it is cracked, peeling, or soft in spots, it is better to remove the loose material first. A putty knife or plastic scraper works well for this. Clean the area with the product recommended for your roof type, whether that is EPDM, TPO, fiberglass, or aluminum. Do not use a harsh cleaner that can damage the roof membrane. Let everything dry completely before sealing.
For most RV vents, lap sealant or self-leveling sealant is commonly used on horizontal roof surfaces because it flows into gaps and forms a flexible barrier. Around a vent, you want sealant on the screw heads, the edge of the vent flange, and any seams where water could enter. If the leak is coming from a cracked vent cover or brittle flange, replacing the vent part may be the better fix than trying to bury the damage in caulk. Sealant can help, but it will not reliably repair broken plastic that flexes every time the RV moves.
If the roof is older or the leak is more than a tiny gap, a peel-and-stick roof repair tape or a proper patch can be a better temporary or semi-permanent solution, especially if the roof membrane itself is damaged. Still, that should be matched to the roof material so it actually bonds. The key is surface prep. Most failed repairs happen because the area was not cleaned well enough or because the wrong sealant was used for the roof type.
After sealing, check the area again after the next rain and keep an eye on the ceiling inside. If you see staining, soft spots, or bubbling, there may already be water damage under the roof surface that needs more than exterior caulk. In that case, it is worth opening things up and inspecting the vent assembly from inside before the damage spreads.
In general, the best long-term fix is clean prep, the right sealant for your roof, and replacing any cracked vent parts instead of covering them up. If you want, I can also help you figure out which sealant to use based on whether your RV has EPDM, TPO, or fiberglass roofing.
