It's the tilt angles that break. Usally in the process I replace both side tilt angles, bridge and cable, however the cable is not always necessary.
There is a bunch of tricks in doing these sliding roofs and if you have never done one, seek professional help. Even if you follow book procedure, you'll have problems.
Mercedes-Benz Master Guild - 2 years
Shop Foreman - 20 + years - dealer.
Part owner - MBZ Transmission remanufacture