Now that you have the circuits, could you employ 3-D printing to build the actual nozzle(s)?
I wouldn't need the circuit diagrams to do that. There's no circuitry to speak of in the actual RCS motors. They operate by solenoid valves, and require only 28 VDC to energize them on. If you've seen the jets themselves, the cable lead is skinny and has only a half-inch Bendix connector. The circuit diagrams are for the control modules that sit between the computer (and the rest of the control instrumentation, such as the SM SEP/JETT switch in the CSM) and the jets. Yes, a skilled aerospace fabricator, with no special knowledge of space flight or of the command, service, or lunar modules, could build a working breadboard of any of the RCS systems using only the information from the operations handbooks. The handbooks are that complete.
To the separate question of whether I could fabricate a new RCS motor of the Marquardt 6-something (the actual model/part number escapes me) type using 3D-printing technology, the answer is a little involved.
The solenoid valves are bolt-on assemblies. I'd have to go check the label to see if Marquardt even made them themselves. I think they did. There's nothing inherently remarkable about the valves. If you've installed a sprinkler system you know what those are. The ones Marquardt used are just engineered to a higher standard of reliability, but don't work materially different than any of the zillions of other kinds of solenoid valves you can find. The thrust chambers were machined from molybdenum and then coated with a molybdenum oxide or alloy (I forget which) to protect them from environment effects and the effects of the corrosive propellants. Molybdenum is a tough metal. I have a molybdenum wrench set (non-ferrous metals are sometimes used to make tools where magnetic effects would be hazardous). It would hurt a lot if I threw one of those at you. The nozzles are machined from cobalt, with integral stiffeners (those ribs). That metal was chosen for its combination of mechanical and thermal properties.
Could these be fabricated today with additive manufacturing techniques? Yes. Not with your home 3D-printer, of course, since the plastics those use wouldn't be suitable. But suitable metals -- including cobalt-based alloys -- are already candidates for additive methods. The most "exciting" (i.e., expensive) methods have fine control over deposition and can achieve a variety of crystalline and grain structures and cooling rates. You'd still have to coat the thrust chamber after fabrication, using ordinary deposition methods, but you could certainly produce the substrate. And since polymer gaskets don't work well in the presence of the propellants, you might need a finish step on the interface between the thrust chamber and the solenoid valve -- the injector assembly.
This sort of brings up the plume deflectors again. Prior to them, the driving constraint on RCS duty cycles was the thermal effects of impingement. With the +X thrusters guarded by deflectors, the driving constraint became the motors themselves, including such things as throat erosion. This is why all the modes except maximum-impulse alternated which thrusters would be employed to achieve the lesser impulses. They didn't want the same jets being used all the time, since throat erosion lessens thrust. They wanted that effect to occur equally over all the related jets. There is a whole universe of control practice out there that flies (pun intended, I guess) directly in the face of Jr Knowing's insistence that it all has to work perfectly or else the LM becomes unflyably unstable.
