Sounds like a faulty bulb. Had a problem like this one on a w140. When you tap it lightly it would come on. You can replace this bulb in less than 10 minutes, with the proper tools. You need a special hook to pull out the cluster from the dash.
There is another way of doing it, if you don't have the tool. Remove the driver's side speaker cover and ac vent. Stick your hand in and push the cluster out of the dash. Remove and replace faulty bulb. Push cluster back into place and install other pieces.
If you are scared of damaging anything, have someone else do it, or go back to your dealer and ask for a reasonable price.