Have just gotten my first Benz, a "91 420SEL. Radio code came with the Owner's manual, but no instructions on how to enter the code. Any help greatly appreciated.

Use the numbered buttons on the radio to enter the code, then change the station to activate it.

Type in the 5 digit code and press seek, should start right up with the stations saved too.

I just called my dealer here in Dallas/Fort Worth. They said that my 89 190E is too old to look up by VIN #. They said they have to pull the radio out, hook up a tool to the rear and play with the buttons and activate it.

Can anybody tell me if this procedure needs to be repeated everytime the radio loses volts? Or does this dealer procedure procure the secret code?

no your radio code should be written on the inside cover of the owners manual. If you give the dealer the VIN # and the radio serial number they should be able to look up the unlock code.