My opinion of Detroit marine diesels is formed by my experience running them. They are noisy, messy and less fuel-efficient than four-stroke engines, especially those with electronic fuel management. On the other hand, DDs are reliable to the point of being nearly bulletproof, easy to service, will burn nearly anything combustible, and once started, will keep on running for as long as you supply fuel, air and lubricant.
For some reason, I've always loved the distinctive high-tempo growl of a Detroit's exhaust note, and I don't even mind their persistent scent of incomplete combustion.
If they are in a boat that checks all the rest of your boxes, I'd say buy it and budget for eventual engine replacements, but in the meantime run 'em 'til they quit.
On the subject of running on anything, my former employer operated a fleet of party fishing boats that ran nothing but Detroits. On the way in from a trip, the mate reported that the fuel tanks were nearly dry - they might quit before the boat (loaded with passengers and their freshly-caught fish) reached the dock. Over the radio, the vessel's owner instructed the mate to empty the galley's deep-fat fryer into the fuel tank. No harm done, and trip successfully completed. Try that with your modern, fancy-schmancy, electronically controlled diesel.
