The BMW M51 2.5TDS is the motor fitted in most diesel Omegas up to 2001 (there was a rare 2.0DTi unit as well).
Its a fairly smooth unit, but underpowered due to detuning to stop it wrecking autoboxes. Easy to rechip to BMW spec (see Omegatoy), but if you have an auto, it will destroy it.
Oddly, I have done an awful lot of research into this engine, and have to agree with Marks_DTM about its ruggedness. Yes, there are examples of high mileage ones, but there are lots of examples of scrapped ones.
Cooling seems to be a huge issue with this power plant. And cooling issues on BMW engines warp and crack heads easily. My own tractor seems like it had an issue with the oil jets to the pistons (cured by some of Omegatoy's magic potions - I ask no questions!), but the overheating that this lack of piston cooling caused wrecked the head. I suspect similar piston cooling may be the cause of the ones throwing rods etc.
I think the lack of oil cooling to pistons is related to the utterly ridiculous service interval of 4,500 miles! Now, you buy a diesel because you want to cover a lot of miles (else it is not cost effective), yet you have to get it serviced every 3 months MAX. I suspect most get done much less regular, hence the expensive damage. Using longer life oil won't help either, as its the particulates in the oil, rather than the oil breaking down (as in petrols) that are the reason for short service inteval.