Buy a new speedo cable (and housing!). The only reasons for it to be unscrewed are that someone wanted to not record milage or it was bad and causing the speedo to jump and rattle.

The line is usually the culprit, but I suppose the gauge itself could be leaking. Should be obvious when you pull the cluster to fix the speedo cable.

The speed sensor for the CC is in the speedo head, cannot work with cable unhooked.

Sunroof can be a number of things -- try to open it (carefully, please) with the emergency crank nut in the trunk. Likely it won't move much because the slides are broken (no lift on that one, I don't think), causing the translation bridge to get sideways. You may have to remove the headliner on the sunroof to find out what's going on, and I don't know how that one is attached (the W124 is clipped to the front edge of the roof panel).

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!