I just bought a sunroof service kit from mercedessource.com and I must say that there is a lot more to doing this right than I originally thought! First, you must use special grease for the tracks. Second, many problems are caused by dried grease and dirt accumulating in the cable tube, which needs to be cleaned out in such a case. The kit includes a cleaning wire and brush (sort of a miniature chimney sweep brush). Then there is sunroof motor, relay, switch, and motor transmission assembly with a clutch. Well engineered, but apparently requiring proper attention after all these years.