1985 300SD Driver Door Unlocking/Locking

[treiberg]

My 300SD will allow me to unlock the driver's side door from the outside, but the other doors do not automatically unlock as they should. However, if I unlock with the key at the trunk, all car doors unlock properly (so the vacuum system and actuators are working at all doors). So what should I be looking for to fix this? I speculate there is a switch in the driver's side lock that is not activating the unlock "signal" for the other doors.