look at the manual, there is a an adjustment that sets the travel limit.
There is also a clutch on the transmission, if loose, the cable can slip.
The nut is just a last resort to open/close the sunroof.

Have you tried tapping the tilt feature?
Push up momentarily on the sunroof switch and see if that will close it.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles