Are you sure this isn't Conrad???
The 1990 version Alpine radio is 5 digits. It can be identified by the two sliding Bass and Treble adjusters under the display screen. The 1991 version Alpine radio is 4 digits, and has no sliding adjusters, but it does have an asterisk button under the right side of the display screen, this is pushed to "enter" the code which is displayed in the LCD screen. These are the only 2 radios used that need a code in a US 190E.
Yes, the dealer can take the car's VIN number, and the radio's serial number, and call the MBUSA warranty dept in Montvale and should be able to produce the correct code.
PS Jackd is correct also. If you happen to know the VIN for the donor car, you could try having a VMI done on that other car and maybe get the code that way. I'd hesitate to buy an MB radio without the card with the serial number and code on it. HERE is the result!!!