This happened to me. The dealer wanted $125 to get the radio code.
Mercedes usually doesn't charge anything to get the code...
Since my car was there for three months for about two days worth of repairs they gave it to me for free. How nice of them
They told me they may not be able to get the code since it is an old car, 1998.
Yet you can get the Mercedes codes for 20 year old cars
The instructions of the radio are in the manual for the sound system.