The black or grey rubber located around the outside of a car door is the weatherstripping but is also sometimes called the door seal or the door gasket. It prevents water from leaking into the cabin of the vehicle as well as reduces the amount of outside noise that passengers hear. These gaskets are attached using glue and, over time and exposure to outdoor elements, the glue may eventually loosen. You can reattach the rubber using automotive adhesive.
Gently pull off the old rubber seal from all the way around the door using your hands. Take note of the positioning so that you can reinstall it properly later. Try not to pull too hard, as this will stretch out the rubber so that it will no longer fit.
Scrape off all of the old glue from the door frame using a wire brush. Use firm pressure, but be careful not to scrape any section of the door that will not be covered by the gasket.
Apply 1 tsp of any glue solvent to a cloth and wipe down the perimeter of the door to remove dust and grease from the surface.
Apply a thin line of weather seal cement across the top of the vehicle door frame.
Place the end of the rubber seal at the top inside corner of the door and press it firmly into place with the flat edge against the door. Continue pressing the rubber into place along the entire top of the door.
Apply weather seal cement along the left side of the door and press the rubber gasket into place along the left side. Be careful to simply press the gasket against the door and do not stretch it downward.
Apply glue and press the rubber onto the right side and finally the bottom of the door. You may need to hold the rubber on the bottom of the door for approximately 60 seconds using your hands so that it does not pull loose.
Leave the vehicle door ajar until the glue cures and is firmly adhered to the door.