I have a 1986 300E, I wonder if it uses the same CC amplifier than your car. Mine works intermittently. I opened it and resoldered all joints, that made it work for 3 days straight. Since then it has been disfunctional for about 3 months. Before that it did not work for a year. If one of your amps works in my car I would seriously consider buying.
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car