Knifer,
I have a 2010 diesel and a mechanical engineer for 45 years. Found the common flaws with the diesel engine as mentioned by others, namely the pre-combustion chambers and cracks in the blocks. The block web (between the cylinders) is 1/8" thick and cannot handle the heat/vibration, prone to crack on the top side then propagate to the lower side. Once the lower side cracks the sleeve O-ring seals leak coolant into the oil. Found a block with no cracks and made a drill jig adding dowel pins in the sleeve plate and block to minimize the cracking. For the pre-chambers I used annealed copper O-Rings (50% softer) to seal the chambers. Can provide more info if you need it.