I believe the rebuild procedure is replacement of bad electronics. Fine PCB soldering. Probably replacement of LEDs or ICs I'd guess.
http://www.jerrytucker.net/ rebuilds them.
Also remember that a lot of Nissan climate control units were used in a wide range of models (Nissan and Infiniti), so don't restrict yourself to Maximas when looking for replacements. You may even be able to swap to a different control unit (most were the same size/shape) if the connectors match...not sure on that one. The equipment involved is interchangeable, though (variable resistor, sun sensor, etc.) so the control units may be as well.
I believe that some control units are "full-depth" (full DIN like a radio) and some are very shallow (less than an inch deep, just the "face"). Not sure if that makes any difference in intercompatibility beyond fitment or not, though.