1990 BMW 750Li Door lock actuator

I asked a question about my door locks jamming in the unlock position and you guy told me that the actuators are toast. I appreciate the feedback but the only problem is that I don't know if I need to replace one actuator or both of them. Both front door locks act the same way when I put the key in them to lock or unlock them. I didn't know if the actuators were on some sort of system that causes both of them to function improperly if only one of them is deflective. I know it's possible but it just seem strange that both of them would be out at the same time. Should I replace both of them or should I test them some sort of way?