Here is a great way to save some money repairing your late 114 and 115 SEDAN vacuum door lock actuators. (Will not work on 2-door coupes). When they go bad it is almost always due to cracks in the rubber diaphragms. Sold in sets of 2. Two are required per actuator and you have three actuators in the left rear door and both right side doors.
Image with diaphragms installed

TO ORDER STEP-BY-STEP ILLUSTRATED INSTRUCTIONS SEPARATELY - click on the link below:
These five page step-by-step illustrated instructions will walk you through the correct procedure of removing your old worn and cracked door lock rubber diaphragms from the actuator housing and replacing them with new ones. These are procedural instructions only. They do not include the parts you may need and they DO NOT explain how to remove the door panel and take the actuator out of the door or trunk.