After a short side trip to test and trace the individual air lines on my caster I have returned to the task of refurbishing the various pneumatic control valves.
The next one to do is the Quadding and Centering control valve. It actually consists of two valves stacked on each other. The outer one (on the right in the photo) is actuated by either A or B air from the paper tower, and its purpose is to prevent air from the C line of the paper tower from reaching the C air pin if either A or B is also selected. The inner one is actuated by the C air from the paper tower, and its purpose is to divert the air coming from the A and B paper tower lines to the Quadding and Centering actuators (rather than the A and B air pins) via the manifold that forms part of the mounting plate for the Unit Shift control valve. From this description it is pretty clear that none of the A, B, or C air pins can be raised for a character being cast for quadding or centering. This is not considered a shortcoming since this feature is intended for casting spaces, in fact, em quads specifically, and such spaces are typically located in the right-hand columns of the matcase, often in column O (which requires no air pins to select).
Rather than risk damaging more of the under-table copper pipes, I opted to clean the mounting plate for this valve in place, so it is not quite as sparkling clean as the plates for the Unit Shift and Unit Adding, but at least it is steel-coloured rather than gunk-coloured. I reassembled the valve using a light oil on the pistons and a heavier oil on the mating surfaces. I left the bottom plate screws just snug until I had snugged the mounting screws to hold the two valve bodies tight together, then I tightened all 8 screws.
The only control valve left to service is the mould signalling control valve.