Do brand new big bore Continentals require top end overhaul at 400 hours?

I've been talking with a guy who is a new owner of a Bonanza. It has
a Continental IO-520 for an engine. It now has over 1800 hours and
he's been looking at overhaul companies. I asked him what he was
planning and he told me that the cheapest way to get an engine is to
buy a brand new one from Continental, but he's reluctant to do that.
He's reluctant because he said they typically require a top end
overhaul at around 400 hours, that they never make TBO. In fact his
airplane's engine was diagnosed with a leaking exhaust valve just a
few days ago and has the cylinder off right now.

John Deakin has also stated his opinion that Continental just cannot
seem to manufacture an engine that lasts beyond 400 hours without
requiring top end work.

My acquaintence is leaning towards sending the engine to a builder
that uses a non stock new cylinder for it's engines, and installs GAMI
injectors as a standard. They dyno the engine to verify performance
before shipping. This "overhaul" ends up costing more than a new
Continental.

So the question is: Is Continental really incapable of producing an
engine that will actually last to TBO?

Thanks, Corky Scott