From what I heard in the other MB diesel list, more than 50% of the 603.97x engines fail below 100kmi. These are used on the 90's S class cars and the typical failure is bent rods and the symptom is oil consumption.

The 603.96x motor has a 5 - 10% of chance of head cracking. These are used in the 86 and 87 diesels. We hear many have had this problems (quite a few forum members have had this problem). Mine does not have this problem, KOW.