Door lock - Vacuum pump problem or not?

[its_snowing]

hi all -

i've got an '85 300sd. one of the problems im trying to solve is a lock issue. i think, unfortunately, that its the vacuum pump, but i thought id ask. i cant get the drivers side door lock to operate properly. i cannot lock it or unlock it with the key, nor can i even lock it with the door open. the only way to lock the door is to close it, and then press down the lock button. because of this, im unable to tell if the auto lock works for the rest of the car, as i cant actually unlock the door with the key.

i apologize if this has been answered somewhere else, but i havent been able to find a thread that deals with this exact same problem yet.

secondarily, im facing the dreaded rear windshield delamination. what does a rear windwhield for a 300sd usually run? i know its devastatingly expensive, but im wondering just how devastating that might be...