Central locking oddity
 

91 300TE 4matic (Gretel):

We rarely lock the doors (not much need 'round here), but when we've needed to, locking the driver's door locks all doors (including rear hatch) just fine. Unlocking the driver's door unlocks all doors just fine.

If the wagon gets parked, unlocked, and all doors closed - and then you open and close the driver's side (left) rear door, all doors lock. Happens every time with that door, never happens with any other doors.

Any clue where I should start looking to find the root cause?

Shouldn't happen at all!

There isn't any signal wire from that door to the CL pump.

Possibly the impact of the door closing is allowing the CL switch in the
drivers door to send errand signal.