If by 'screen position' you mean the angle between the display and the case, you have just identified the cause of the problem. The flexible PCB that forms the 'cable' from MLB to display either has poor connections (at either end) or has cracked, broken, been torn or corroded at some point in its length. Correction of the fault requires disassembly of case and display, taking care, because the 'cable' is coiled around the display clutch/hinge on one side.
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