This page describes the VW Gamma 5, a cassette radio for the European market manufactured by Sony. Note that there are different radios named Gamma 5 (see the index).
Gamma 5 uses a Renesas (NEC) uPD78070 microcontroller, which has an 8-bit CPU using the 78K0 instruction set and has code in mask ROM. I have not extracted the code yet.
This radio has only begun to be studied. Some KWP1281 protected KWP1281 commands have been found through experimentation. The SAFE code is stored in the EEPROM using some form of encryption that is not yet understood.