1980 300D Door Locks

Greetings !
I am new to this site, and new to MB also.
I recently aquired my 1980 300D. If seems to be a solid car however I am finding its quirks. I think I have a vacuum problem, but one thing that I am stummped about is the door locks. I cannot get them to move up or down. This is on all the doors.
I have not removed the door panels yet, I would like some feed back before I jumo into it. I have the Mighty Vac tester & guage and I am ready for action.

Robert