Newdent A few years so I’m told by the previous owner. Judging from my first use, they were tightening the valves into they locked.
That can’t over compress the seat because of the way those valves work…they are closed by spring pressure, not how hard you turn the knob. I wouldn’t have thought yours is old enough to need a replacement seat…I would expect a decade or so.
Take the valve apart and clean the seat….when eventually the seat wears, you can probably turn it over to the unused side.
P.S. Unless they were super ham fisted and bent the bejesus out of the circlip part no 9400001…usually though that’s bent the other way through opening it hard to the stop (that circlip), as I don’t believe it could be bent the other way.