My own '84 240DL has it (it's still running, with ~218K miles), and that should include operating your tailgate lock as well -- although that tailgate lock, license plate lights, and defroster grid is problematic because the wiring harnesses to the tailgate's electrical doodads often break from years of opening/closing the hatch.

However, in your case (based on your question) it seems the entire electrical locking system has quit, rather unusual. Most often, it's one or another door that doesn't work, not the entire system. So I would suggest looking at those components common to the whole system, including the fuses, the actuator (in the driver's door), and the wiring (in the driver's door) -- since the driver's door contains the master controls.

Good luck.