Older farm equipment are often overbuilt, heavy-duty, and reliable as a rock. Depending on the brand, spare parts could be cheap as dirt... or unobtainium.
Newer equipment tends to be more plush (for the operator) and easier on the environment.
One HUGE difference between older Diesel engines and newer ones is the emission-controls. In general, the ol' super-reliable engine designs were replaced with emission-friendly engines. The newer-engines demand more preventative maintenance and generally have niggling problems not seen on older engines.
These newer, emission-friendly engines have proven to be SEVERELY less reliable than the older engines. Infact, the world-renowned CATERPILLAR diesel engine company simply STOPPED BUILDING engines for over-the-road trucks because of emission regulations. (but their locomotive engines are world-class)