Replacing the Third Brake Light and Preventing Cab Leaks on a 2005 GMC Sierra 1500 storeboard.com

You have two options for the replacement light: a complete OEM-style third brake light assembly with a new foam gasket, or an aftermarket LED unit. The LED option is highly recommended because it is brighter, responds faster, and lasts virtually forever. However, do not rely on the thin foam gasket that comes with most replacement lights—it will fail again within a few years. Instead, upgrade the seal. Purchase a sheet of closed-cell foam rubber or silicone rubber (1/4 inch thick) from a hardware store. Trace the outline of the new light housing onto this sheet and cut a custom gasket. Alternatively, apply a bead of high-quality outdoor RTV silicone (clear or black) to the mating surface of the housing. Allow the silicone to skin over for a few minutes before installation.