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The problem you have is definitely the lock actuator itself and it will need to be replaced. This actuator comes as a sealed component and it cannot be opened (except with a hammer) :) It is located on the latch piece but is held on by 3 screws.
I've actually opened the actuator recently and reassembled it. Is there no way to purchase just a component part? And what about my switch issue?
You can get the actuato by itself but just was sure how mechanically inclined or experiance you had. Here...
Also if what you say here... Actually, the driver side door lock switch will lock all of the doors, but will not unlock any of them. Then start with the actuator and before reassembling check for power and ground at the switch itself. If they are good then the master switch will also need replacing.
Please reply back if needed.