First, the second option John HD said.
No repair is better than the right repair. Patch work repair is not as good as the right repair. 'Nuff said.Now....
Drill the old rivets.
CAREFULLY, using a GOOD stiff putty knife, remove the old vent.
Clean both sealing surfaces; leveling these surfaces as much as possible.
Clean both surfaces.
Reseal using Vulkem.
Rivets have two or three possibilities; there is an aluminum pop rivet available, that has a SEALED rivet portion. IT WILL NOT LEAK. It does not spread out behind the panel as does am Olympic rivet. Do not use it if your rivet holes are enlarged or sloppy.
All in all done in this manner, the unit will not leak for many years to come.
Also, your vent cover should have the foam style gasket between the cover and the vent housing replaced as well. Clean both surfaces well. The foam will stick to the vent cover with the adhesive strip that comes already applied to it.
The best cleaning agent JUST BEFORE applying Vulkem or the foam tape is denatured alcohol.
I wish you much success in your reapir.
2000 390 Landyacht XL
1989 29' Excella
WBCCI #6673 jerry Hodge
Have no intention of arriving at the grave safely, but rather to skid in sideways, chocolate in one hand,throttle in the other, totally worn out and screaming
"WOO HOO, WHAT A RIDE!"