"It seems odd that if the owner is on board that the vessel would continue to be abused. Darwin at work?"
Sadly it is the working requirement of the vessel , not ignorance.
It is simply part of the cost of running the boat ,, built into every fish you eat.
Perkins are in many Brit delivery trucks and taxi cabs.
Deere uses Jap tractor base blocks to marinize.
Replacing a vibration damper is done on many diesels based on operating hours.
Like filters , injectors and pump impellers , another expense , no big deal.
The future will be interesting as the hammer of Gov continues to shrink the number of base engine mfg.
With world wide use of " clean air " requirements our boat sources will continue to get more complex , more expensive and less reliable.
In the OTR world it is now common for owner operators to purchase a pre 03 truck , and spend almost the price of a brand new truck in a total overhaul.
Pre 03 engines give better mileage and can be repaired.
A factory new truck is replaced if it doesn't work, not cheap to do.
Happily the dead hand of gov is concerned with larger engines , and the small stuff 1 to 6 GPH is a few years behind in the "clean air" rules.