I had the exact same problem with my 95 E320. The front of the seat is raised and lowered by a motor connected to a flexible drive shaft. The drive shaft very much resembles a speedometer cable--outer housing with flexible inner shaft. Inner shaft has square ends that engage motor on one end and drive unit on the other. In my case, the inner drive shaft slipped to far into the motor end. As a result, the square part of the inner drive shaft was no longer engaged in the drive mechanism. I inserted a 1/4 inch piece of piano wire into the motor drive end and then reinstalled the drive shaft. The 1/4 inch piece of piano wire prevents the inner part of the drive shaft from migrating to deep into the motor end. It has worked flawlessly ever since.

Figure 2 or 3 hours for this repair because the seat has to be removed. Once the seat is removed, the drive assembly is accessible from underneath.

Hope this makes sense.

J. M. van Swaay