I guess the key here is discovering what are the typical failure modes for these units, as well as the specific failure mode for any individual one unit.
I will need to be dealing with this issue myself, although I have not yet actually done a physical inspection of the throttle actuator that is on the recently acquired 94 E420.
If the failure consists of deterioration of the insulation on the external wiring, perhaps that can be resolved in a rather straightforward manner. If the internal potentiometers and/or switches become fouled or dirty, perhaps disassembly and cleaning with the proper solvent (TV tuner cleaner?) may work. If the traces on the potentiometers are worn through, then you're pretty much screwed. Once again I have to state I have not actually looked at the unit yet, so I'm flying blind here -- disassembly & reassembly may not be practical.
And because we live in such a litigious world, I guess I should state the obvious. This is a highly critical part; failure could have dire consequences, therefore any attempts at repairing these units would of course only be done for the purposes of testing the theoretical feasibility, and of course the ‘repaired’ unit would never actually be used on an engine that is actually installed in a car.