Frode Berg wrote:

He said this is the way it works in the US.

That's the way it works for many aircraft. There are certain types of businesses
that have to have the engine overhauled at the service time specified by the
engine manufacturer, but others don't have to do so. Note that the engine is
usually overhauled. Few people replace an engine with a brand new one, and the
regulations don't require replacement with new. Many individuals who own aircraft
will continue to operate the plane until the engine starts to give signs of
wearing out. These signs would be things like using too much oil, oil fouling
the plugs, poor compression, and so on.

Also, what are the safety issues?

Older engines are more prone to failure. I've read, for example, that this is a
big problem with the Douglas DC-3 as new original engines can't be bought anymore.

Does a new engine actually perform better?

An overhauled engine should perform as well as a new one, and some shops produce
engines which they claim are better than new.

He told me about a C177 that came to his shop from the US for overhaul
(change of a couple of sylinders +) and it had over 9000 hours on it's
engine...

It's possible for an engine to last that long if it were overhauled several times
during that 9,000 hours. It's highly unlikely that one would live that long without
an overhaul.

George Patterson
Great discoveries are not announced with "Eureka!". What's usually said is
"Hummmmm... That's interesting...."