Another thing you can check is that the display holder bolts are not too tight. They are intended to be loose enough to be able to rotate the display to reduce glare. If they are too tight the could cause the display mounting dock to bow and the connection might not be firm.
If all this isn't working it could be time for a new display mount. That's really the next logical step and in my experience it's the likely culprit. Fortunately you should be able swap it out without running the wire to the motor. There are little screws on the underside that attach the wires. But I would recommend you bring it to a shop if you can.