My boat is equipped with the 54hp, 4JH4E. Yanmar makes great engines, low maintenance
if regular service
is performed and extremely reliable. Less expensive to run than Volvos (parts cost...)
Accessibility to components is more of a boat specific issue. Some builders just try to cram the engine into the smallest of places, hence problems such as Vasco mentions.
And yes, engine mounts are often the key to a smooth running, problem free (read vibration free) engine.