The original "chassis" it was on died.
The central stem was tacked onto the round base and had started to tear the metal (quite badly).
I was going to buy a new donor and repair it, but it seems the norm is now NOT to weld the central stem and just have it located in the base - makes sense - less space in the box and perfectly fine but a bit shaky for such a tall and heavy chair.
Samantha also moaned about the weight (it
was heavy) and with the new floor installed I didn't want to have it dragged around. Jensen also took a shine to the old one and I frequently found him trying to scale the side of it (it wasn't really stable enough for that).
So, in short, it's been replaced with a lighter, shiny chrome bar-stool (that fits in with the new flooring and decor much better)