You might want to try whatever will work for you. I don't know what kind of '79 MB you have. I haven't seen any screws on my door panels in my 300D. I just guessing at what you can try. I've never tried taking my door panels off with doors open or closed.
The other thing you can try is getting hold of a "slim jim" and try to open your doors with that. You don't need to have door lock buttons to use one.
Good luck.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012