I'm about to purchase a 2002 MB A Class Japan made and it cannot start, the mb mech diagnosis is " Serial Communication Error". He then said it could be the ECU, Immoberlizer or the Round Key Sensor thingy. He came back and said it was the immoberlizer and it would cost me $420, plus $200 repair charge. He said the immoberliser has a chip on it and it needed to be replaced. I have no knowledge about any of this, but non the less, could you please help me? This is the chassis : WDB1680321J324315