m103 is a motor that almost an mechanic can work on. But, early m104 does have some problems that you want a certified tech eg head gasket and wiring harness. m104 does have more power but at a higher operating cost. But if you find an impeccable m104 go for it, likewise a 300E. I have both motors m103 in my 89 300e and m104 in my 97 e320.