This was something I learned early on after buying my 40. It was shared on the old Luhrs furum so I want to share it here. Make sure you caulk the rub rail all the way around , top and bottom. I had a mysterious leak coming down my port side galley wall. It was from the lower side of the rubrail. The bow rail mounts are also known to cause problems.
This is a common problem with all used boats. Many rub rails leak . And they are hidden at times until water or rot starts bleeding through the wall covering or bulk head etc. It's also somethings the ''Oh mighty supreme sureyors'' out there seam to miss, nor bring up. Among other things they tend to miss....
I just discovered that my run rail is leaking after trying to find the culprit of moisture in my forward stateroom for the past year. anyone know the best way or any tricks to re-caulk it?
Mask off the top and bottom of the rub rail as it sits. Remove it. Clean the surface and etch it with sand paper being careful to not disturb your tape. Lather the area with a UV sealant, color and bond of choice (Sikaflex is a good choice). Use plenty of sealant so that it presses out when you reinstall the rub rail, presses out both on top and bottom and also seals the screw penetrations. Clean up your mess and move on to the next section. Excess sealant can be recaptured onto a ziplock bag or container and reused on the next section if you're moving quickly. It's a pain in the ass, but you aren't stopping the problem with a bandaid.
No tricks ...What the Burger King (rtafford) said. That is the only way . You have to get behind it to seal it properly.
Agreed on the Sikaflex. We just replaced all the old caulking that was yellowing with that, including all along the rub rails, top and bottom.