22K
That's super low. Since you mention that the odometer doesn't work, it may be possible that someone (not accusing only suggesting) tried to alter the mileage and messed up one of the gears or another part and caused it to stop working. Typically, the odometers work for a long time before they fail. I know that the speedocable wears out with time, but I haven't heard of one failing before 100,000 miles. You could run a carfax on the car. If the car is a local car, you could call the local MB dealers in your area and give your VIN to a someone in the service department to see if they had any history on the car.
Good Luck.