I have a single FL with 7,000 + hours. I've placed 3,000 hours on it in 20 years.
Have not suffered a single breakdown or failure to start.
I replace the accessories; heat exchangers, impeller, pumps, hoses etc on a schedule.
Parts, as others have mentioned, is ridiculously inexpensive compared to other engines, so replacing accessories prior to failure is doable.
The engine is a simple design, simple to work on.
I drilled and tapped the drain on the injection pump and added a hose to facilitate spill free injection pump oil changes. Having to change the pump oil while on a cruise is inconvienient but the hose makes it more tolerable.
In addition to American Diesel, Harbor Service in Everett stocks most Leman parts and Pat's Engines in Seattle work on them for Pacific NW boaters.
Mike at Harbor Service worked with Norm Dibble at Doc Freemans and Norm went to work for Pat when Doc Freeman closed. Both individuals are knowledgeable and very helpful.
Norm Dibble was the West Coast Lehman guru and conducted his famous Lehman seminars for years in Seattle prior to his death.