I think there was an article in the MB club STAR magazine a few years back about rebuilding seat pads - looked rather simple - may be able to go to the MBCA site and archive the story.

Also the most recent issue of Mercedes Benz Classic magazine on the newsstand (Barnes & Nobel ) now - page ninety has an excellent story on leather care, repairing hole, relacquering seat - not that you would do the work yourself but a good guide.