Those servos can be fixed. My moms 05 ZX3 has a dealership installed cruise control, and awhile ago the cruise stopped working. I had dealt with cruise control problems in the past so I knew what was involved, and after finding no problems elsewhere I looked at the servo and shook it and could feel/hear parts loose inside the servo box. Took it apart and found that some screws had come loose from the plastic gear mechanism. Fixed it easily and it works like a champ now. The one in her car uses an electromagnet to pull on its throttle cable and the servo was actually mounted on top of the engine on a rail, I know factory installed are not as accessible as that.
Mccreet, you have any luck with that self diagnostic procedure?