In most instances, the best way to repair a leaking roof vent is to replace the vent with a new one. Roof vent boots are made of plastic or metal, as of 2015. With plumbing vents, the rubber gasket that surrounds the pipe weathers and deteriorates leading to leaks.
When homeowners find vents on the roof that are leaking they often try easy repairs. However, most of these easy fixes do not work. Duct tape, caulking and even roofing cement only offer a temporary fix.
To repair a leaking plumbing vent, carefully loosen the shingles surrounding the boot, remove the old boot and discard it. Install a new boot around the vent, making sure the rubber gasket around the pipe fits tightly. Use metal roofing screws with rubber washers to secure the boot to the roof, and then reinstall the shingles around the new unit.
Leaking air vents from the attic require a similar approach as vent replacement. With the attic vent, it is usually possible to remove the nails from either side of the vent to free it without having to remove shingles. A similarly sized new vent should slide into place for attachment with the rubber-washered screws. Check the remaining vents in the area to ensure they remain secure.