"Damper"
The rubber seal is the reason I made sure all the new inserts are flush, and luckily mine is in very good condition with no signs of water ingress even with only one screw holding it together. If that seal was showing any sign of compromise then I would definitely have replaced the lid
Its about £40 so even if you only rescue the bottom piece its still a saving of £50-odd and a huge amount of swearing to get it out.