This is a very common problem on these older Mercedes. That crumbly putty looking stuff was actually a plastic ball that was part of a ball and socket joint that the linkage pivots on. You can buy a replacement assembly right here at mercedesshop.com-

http://catalog.peachparts.com/ShopByVehicle.epc?q=&yearid=1982@@1982&makeid=MB@@MB@@X&modelid=240-D-002@@240D&catid=C@@Fuel+Injection&subcatid=C7030@@Throttle+Bushing&subcatid=C7030@@Throttle%20Bushing&applicationid=000012095&mode=PA&source=www.peachparts.com&clientid=catalog.mercedesshop