I had Clary's transmission shop (an independent in Seattle I've done
business with for many years, they know Subarus as well) do a flush on
my '00 OB at 99K miles as I bought it with 95K and had no service
history, just to ease my mind.

About 8K later, it developed the known 4EAT quirk of hesitation doing
into a forward gear when first started cold (goes away on warmup).

It's something to do with an aged O-ring that doesn't seal as well when
the gunk gets flushed out around it from the power flush. It's not a
disabling problem, just an irritation.

Rather than doing a teardown on the tranny, they suggested adding a can
of Seafoam transmission additive every 6-8 months.it swells the seals.
That works, I just dump in a can when it starts acting up. I can live
with this...

There may be other tranny additives that would work, but I'm not going
to waste time finding out. Seafoam brand stuff isn't stocked by Shucks
or Autozone. I get mine at NAPA, you may have to find a "more
professional type" autoparts store if you don't have a NAPA store nearby.

I'd still go with the flush, just be aware that it may cause problems.
There have been some instances where a flush uncovers a serious problem
that was going to occur anyway, the flush just accelerated it.

Do it again. You're doing just fine.

In my experience, 'flushing' just flushes your wallet of cash. When I was
working for a dealer (used cars) we had two trannies flushed. The first
one waited until we sold it, and then failed about a week later. The
second one had to be flat-bedded about 1 mile from the place that flushed
it.

If the fliud is still, um, at least 'reddish', doesn't have black in it,
and isn't brown, drain and refill again. If it's brown, drain it, fill it,
drive about 3,000 miles and do it again. If it's black, put a Crepe on it,
it's dead... (I had a tranny run 12,000 miles like that..DON'T TOUCH IT!!!).

60,000 miles is about right for a drain and fill. You should be in good
shape.

If you're particularly anal about it, you could disconnect the high
pressure side hose that goes from the tranny to the cooler in the
radiator, with the wheels off the ground start the car, let it warm until
the idle comes down, put it in drive and put the hose in at least a one
gallon container. Five gallons is better. Keep adding tranny fluid to the
inlet as fast as it is running out of the hose. When the stuff running out
of the hose looks new, stop everything, reattach the hose, check the fluid
and add more if necessary. I think you can do this in neutral, too, but we
always did it with the drive wheels off the ground and turning.