somethings not right then, its a plastic sleeve; have you ever stripped the post out and cleaned it? how old is said bike, has the seat sleeve ever been replaced?
I am down in wellington if you need any assistance; thebromptonman.com
I’ve had it 5 years, it’s had a service and a Brompton warranty repair on the front end. I’m probably just gonna get it serviced soon by my local Brompton dealer. Last service was pre Covid.
I a weird way it’s my favourite bike and I have put it through the mill. Sleeve probs knackered
Because it seizes