616/617 - Its only issue is that it is so awesome/reliable that the engine will probably outlive you. I've put 100k on mine and it still runs as good or better than when I got it.

601/602/603 have more tendency to headgasket issues but are still excellent engines

early 603 the head can crack if temps get too high

603 3.5 liter = rod bender engine, but the heads are good

the later engines also seem to suffer from more fuel leak issues than the earlier engines.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)