Dave,
1. Since purchase of car, ALWAYS used key fob remote to open/close car.
2. Parking lot accident damage in that area (leading edge drivers rear quarter and immediately aft of door handle.
3. Discovered after body shop repairs were final that I couldn't manually lock or unlock door with key.
4. "Crossfire tech" at Ontario (CA.) CJD (SRT-6 here on the forum recommended) diagnosed problem as drivers door actuator (discontinued) was at fault. Informed me that OEM part was discontinued and gave me the p/n stamped on the actuator and advised that I could get the actuator via MB with that number. WRONG.
5. Finally took everyone's advice and located a reputable independent MB mechanic. Turned out the connecting rod from the lock cylinder to the actuator had been disconnected and tucked out of the way (suspect body shop). Rod connected, manual locking/unlocking GOOD.
6. Was advised that there is damage to a spring in the latch and it would be only a matter of time before it goes and the latch would need to be replaced.