Problems with the pneumatic system can cause closing assist and door lock issues.
Car Problem Reports
Mercedes-Benz 500SEC Closing Assist/Door Lock Issues Due to Pneumatic System Problems
Mercedes-Benz 500SEC Problem
Model Year Affected: 1993
Visitor, 1993 Mercedes-Benz 500SEC, 160,000 mi
The locking system does not work window will not autoseal when door close and truck will not come up to where it should go down auto as well .when the door is locked by remote the door just blinks about 6 or 7 times when green or red.