Look to the sides on the rear of the sunroof lid. There should be some plastic guides behind the track that a metal piece attached to the lid slides up to make the lid close. The metal piece on the rear sides of the lid has adjustments. Your headliner will come off as you probably know. When the lid is open it sort of slides up and out the opening.
Once you are to the 99% closed position with the head liner for the lid off, try and gently push up on the lid in the rear to make it close completely. You may have to use the switch in conjunction with pushing up. Then proceed to make adjustments to make sure the adjustable metal piece on the lid corner is catching on the plastic part next to the rail to make it lift and close completely. Then open and close the roof and make adjustments to the side sliders and the rear lift parts until it operates correctly. Once it is working right then slide the liner through the top of the roof and back into place.
It is possible one of your tabs on the rear corner of the lid the that catches in the plastic part by the rail is bent. You can remove it and straighten it if needed. Replace if necessary. I will be working on my roof soon so maybe I can get some pics. The roof is basic once you figure it out. I hope this helps. BTW, I don't think you need a new cable.

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Chris
84 280sl
82 300d euro