Thom, the early ABS systems aren't very complicated. Wheel speed sensors, power supply to the control unit, and solenoid valves/relays at the hydraulic unit are all possible causes. On early 124's, improved wheel speed sensors/hardware are available. From your description it's impossible to say for certain what your problem might be. The only sure way to find out is to have the system tested by someone familiar with the system (not the mechanic you mentioned in your initial post!!!). Good luck