Toilet seat bumper

This may not be an instantly obvious fix but....
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We live in a house that's nearly 200yrs old... and some of the amenities are slightly dated. One of the ways you notice is that modern toilet seat covers don't quite work as well as they perhaps should.
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Imagine being a gent going to the loo... you lift the seat with your Mrs in mind... as your mother taught you (she'd be ever so proud). And then... right as you "get going" the worst imaginable thing happens... The seat starts to descen