Go to http://dieselgiant.com/repairyourodometer.htm. There are excellent step-by-step, pictured instructions "How to Repair Your Broken Odometer". Though this applies to 1974-1980 models, I found it very appliccable to my 1983 300SD, and I suppose it might give some clues for your model as well.
The cluster is a pressure fit and pulls out. Easiest to remove the lower dash and push gently from the back. They sell "cluster" tools, but not necessary. Also easiest to remove the steering wheel for wiggle room (not necessary but a lot easier). The steering wheel is a 10mm Allen wrench. Easiest with a socket drive and 3" extension.