I'm not a diesel mechanic by any means, so I don't really have quality information.
My 22 yo Yanmar seems to be doing just fine on normal maintenance. The only thing I have done in the last 16 years is replace the impellor on the water pump (once), fuel filter (twice), and both injectors once (for preventive maintenance).
Outside of that, it's been changing the oil and oil filter every season, and filling the water intake with anti-freeze in the winter.
The engine is a bit hard to start when it's cold out (like under 50 degrees), but never a problem when warm.
My boat has always been in fresh water.
