Ceramic coatings for your paint. Many different brands out there, but it is labor-intensive and requires a thorough correction of the paint before application. If you're not able to endure hours of manual labor, then you'll most likely not do this. I use CAR PRO CQUARTZ. I have been in this market for many years doing ceramic treatments. I am 59 and retired now and only treat my cars. It's a fantastic product to keep your ride looking shiny and protected. Newer technologies are available today that surpass ceramics. It just keeps evolving.
However, you can use a simple wax for your paint to coat over the camera lenses. Not to say that it's leaking from the lens itself. It may be leaking from around the camera housing. You'll need to be sure you wipe all the wax off due to the chalky ingredients that can leave a white powdery residue in the cracks and joints. It might work, or it might not. I can't say that what I did with my ceramic treatment did anything to keep water out. I was just thinking this through logically and coming to a conclusion that the ceramic coating could have, and most likely did, offer an invisible seal around the camera lenses. Ceramics are extremely hydrophobic and repel liquids up to about 110 degrees or more of contact angle. I don't see anyone else here having the issue you're having, so what I'm saying to you may have no valid point. It's just a logical walk-through. Try a little wax that you would put on your paint to protect it, wipe it off thoroughly, then see if it still leaks. I would be curious to see if it's a solution.
Keep in mind, the cameras are designed to get wet. They are in locations where they will get extremely wet, so what the dealer said is odd. I'm no technician, but it seems there would be something else going on there.
