The rear window on a convertible top will sometimes be glass. The glass seal is a "soft seal," meaning that it is not fixed to any sheet metal. Over time, the window seal may separate and begin to leak. To fix this, reseal the glass using a urethane sealer made for automotive glass. These sealers can be found in any auto parts store.
Apply a thin bead of urethane sealer to the glass edge.
Use the applicator to spread the sealer against the glass edge and to seal the glass around the convertible's rear window.
Use a rag to clean up any excess sealer that has got onto the glass.