My 84 300SD door locks only work manually, not the way they are supposed to. I haven't had time to troubleshoot the vacuum for it yet. However, my driver's door lock will not press down either --- with the door open. I can shut the door and reach in from the open left passenger and manually lock it fine. I can also manually lock it with the key.

I know it doesn't solve your problem but hopefully it is additional information.

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99 e300
98 e300
90 Suburban 1500 4x4
92 ZR-1
04 Tahoe 4x4
05 Scag 52" zero turn
97 e300 - totaled on black ice
84 300SD - gave to a friend
85 300TDT Euro - SOLD to my little bro