Fascinating!

It really does look like a quality build. If you are happy with the machine, then I imagine a paid repair would be perhaps UK100 or less? Worthwhile up to even a bit more than that.

As others have noted, that fancy air pressure control gizmo looks like a good candidate for replacement, given that the pumps are all otherwise working. You could take a chance on swapping that for a new one (easy access for that), or just pony up for a repair person to do a diagnosis and replace whatever they discover to be failed.