On the W126, that is a single line system that provides both pressure and vacuum from the pump. Easy enough to check by pulling the cover off the "B" pillar and using a mightyvac pump to see if the line holds vacuum. It may be something as simple as a flex line at the actuator.

However, I'm with Sixto on this one. If there is virtually no tension on the actuator when switched to lock, I would inspect the actuator for something mechanical that may have come loose.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )