I know you have tried to close this thread a few times, but thought I would chip in my $0.02 worth.
I have the same engine as you, the 5416, fitted to my Bristol 29.9. I recently did a complete rebuild and overhaul of the entire engine, (but not the transmission), replacing or refurbishing every component that showed signs of wear (or in the case of my engine, damage).
I wanted to pass along two things:
These are old but simple, solid engines that can be rebuilt by anyone with just a bit of mechanical inclination (I had never touched a diesel before), and parts are readily available from Kubota dealers and online Kubota sources at reasonable prices.
There is at least one weakness I know about - the raw water pump. If the seals on this pump fail, raw water will be admitted to the crankcase. This is invariably not a good thing.......
I'm not a mechanic or anything like one, but if I can be of any assistance with details on the engine or parts, don't hesitate to ask. Sorry I don't live in your neighborhood, or I could help in person.
1980 Bristol 29.9