Hi, and thanks for visiting my page. I sell used parts for Daihatsu DM950D engines as well as other brands and models such as the Yanmar 3TN66 and Briggs Diesel parts. Since I run all of these engines myself, I can answer some of your questions.
As you may already know, these are not very reliable engines. I have found they do not often make it past the 1,500 hour mark. However, they do run well for a while and crank out a lot of power for that small block.
The weakest links in the engine are head cracks, when a small crack develops between the exhaust valve and a pre-combustion chamber due to overheating; broken rods–usually for no reason; and premature cylinder wear. I have not figured the cause premature cylinder wear, either, but I see it often.