Sound like a the angle is jammed. Is both attached to the black cross bar? If so I would suspect a crushed angel but let see once you get it opened. Try to help the angle that doesn't move. It should be firm but not jammed.

What happens when you run the motor? Does the cable move at all? Try to help it by pushing cross bar backwards..once angels drop down the roof should move quite smooth. If not maybe the rail are soaked in old grease(wrong kind of grease.)

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'87 MBenz 190E 2,3 8vlv