No 'gasket' kits available.......non replacement item.
New doors only
Clean the frame surface
Clean the gasket face
Make sure doors are sticking frame evenly..have not slipped/sagged down. (worn hinge bushings)
One other thing you can try: (last ditch attempt)
Place a ball of cotton in each corner under the gasket
Then heat gasket material until warm....using hair dryer. Takes a while due to size of gasket....get it warm
Then close door and let gasket reset......20 mins. or so
Then remove balls of cotton form corners