I remove these vents a lot when installing solar charging systems on Airstreams, as we run the charging lines down the refrigerator vent stacks.
Drill out the rivets and remove the vent. Line the bottom of the vent where the rivet holes are located with butyl tape sealant after cleaning the surfaces well and then re-rivet the vent cover back in place.
Complete the sealing process with SikaFlex 221 polyurethane sealant, running a bead over the rivets and the outer seam. Spread carefully and smooth to your liking with a very small plastic putty knife or your finger (encased in a rubber glove), as this stuff does not like to come off!
You will never have a leak there again if properly executed.