Turns out that one needs the radio AND ignition on for 15-30 minutes before the LOCK changes to CODE and then the code number can be entered. Came that close to buying a new replacement radio. Accidently fell into the solution when on a long drive (going to the grocery store wasn't long enuf) I tried to mess with the tape player to see if it too was locked out. It was. Left the radio turned ON and after a bit I looked down to see the word CODE appear, punched in the numbers and voila.

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1993 MB190e 104k