My understanding of the 99 2.5 is it is a one-year only design.  This
makes parts expensive.  Also has a history of head gasket failures.
Can't remember if the gasket develops an internal or external leak.
Also been told the vast majority of this engine will run forever
without problem.  You only tend to read/hear about the ones that have
the head gasket problem.

If the head gasket has been done, you should be good.

If not, it will likely need doing sometime, circa $3K.
If it overheats badly and cracks as well, it will cost
even more (new head or engine).

If you want to postpone the time when this *will* happen,
ensure that you find a serviceman who knows how to bleed the
air when the coolant is drained, or google it up yourself,
and ensure that it *always* happens when needed.

The problem with the EJ25 engine design is that the water
pipe that takes coolant over the engine from one side to
the other *traps air*. When the engine is run, the air
moves to the head on one side and you get hot spots leading
to HG failure.

It's possible if you're keen to tap a small nippple into the
top of this crossover pipe, and run a tube back to the radiator,
which will allow the air to bleed out properly. There's a guy
who uses an EJ25 engine in a homebuilt aircraft who diagnosed
the fault and used this fix; google for his page on it.

We still have our '98 Liberty (Legacy outside Australia), and
the engine needs significant $$ spent to fix various oil leaks,
but the HG was done 4 years ago and has been ok since.

Clifford Heath.

I hear they usually go bad at about 140k miles.

Just kidding, but they've gone bad with less than half that mileage,
and also lasted to 200k. It's a gamble.