If it is like the w126 you can do a search for that and see if the proceedure sounds familiar. It seems to me you access the cable from the trunk and manually unwind it. I think you also have to remove or drop the back headliner to gain access to the mounts. Hope this helps.

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If it ain't broke take it apart and find out why.

1983 300SD, 4 speed
1994 C280
1987 300TD wagon
1996 HD Road King

Ride in Peace Eric Peterson, Harley of Macon