Finally, the flap door in my Nikon LS-9000ED scanner got broken during a recent scanning of film. It came out all of a sudden and fell on to the floor when the film holder was moving in and out during scanning.
I immediately posted a message on Facebook Nikon Cool Scan Users Group and got a reply there to contact Gleb Shtengel. I got his reply and then I ordered a replacement flap door from him. The response was very quick and the shipment arrived very quickly.
Then I started following the instructions here and replacing the broken flap door.
I hope this scanner can still work for another 20 years!