I have a set, the official Mercedes Benz set, for the W124 that I will sell to you for $100 + actual shipping if you are interested. The jewel case has been opened, and I have run them in the computer. But the CD platters have no markings or smudges.
I solved some complicated wiring issues using the Electrical Troubleshooting Manual and don't expect to need them again anytime soon. In my opinion, this is the best collection of information for the W124.