It's not wise to generalize the advantages of synthetic engine oil to synthetic
transmission oil, for the following reasons:

1. The major advantage of synth engine oil is reduced friction. However, ATF must
NOT be too slippery; it must be possess the right degree of "grabbiness".

2. A major advantage of synth engine oil is its ability to remain much more fully
effective as it becomes diluted/polluted/contaminated by combustion byproducts,
which does not pertain to ATF. Compared to the harsh environment in which engine
oil lives, ATF lives in a bubble.

3. Except for towing a trailer in hilly terrain, or racing up Pikes Peak, the ATF
in our cars loafs; it is not highly stressed, either thermally (good cooling) or
physically (the TC is nearly always locked up, except [briefly] in 1st gear).

I've run my car hard up Pikes Peak (my prev car, which had no such heat shield
over the turbo, had the turbo housing glowing pale red after similar but slightly
slower runs halfway up the mtn). I let this AT flush its own ATF at 61K mi.
There have been fewer real hard runs up PP since then, but it's been 70K mi
since that ATF flush and the AT/ATF is still just fine; I have no current plans
to do anything with/to/for it.

So my recommendation is to not waste your money and -- if you feel the need to
do ATF maintenance at all -- just let the AT flush/replace its own inexpensive
Dexron every 70K mi when the car is preventively taken out of service anyway for
timing belt repl. That seems to be more than enough to keep the AT/ATF happy and
healthy (though my car does not regularly see ambient temps over 100 dF), making
it a good compromise between the over-maintainers and the never-maintainers.

The paradox is this: if you decide the ATF is feeble and needs to be somehow
fortified, will you then want to let this more-expensive, fortified ATF stay in
there forever? Wouldn't you be better off replacing the cheap std ATF every
3-5 years than leaving the expensive stuff in forever? (BTW, if you're one of
those folks whose accountant will tell them to get a new car in 3 years anyway,
you won't keep your car long enough for any of this discussion to really matter
to you. We had one poster here who actually drained a little ATF out and topped
it off with each oil change. This is probably the worst thing you could do to
your transmission. But he got a more expensive car before the warranty on his
850 expired...) And if you have so much money that you can afford to flush
(treat as disposable) the expensive synthetic ATF, then I don't really believe
that you are losing any sleep worrying about the remote possibility of being
stuck with an expensive transmission repair anyway. (If I'm wrong about this,
you should consider buying extended warranty coverage, and also a lot of lottery
tickets, which also seem like a good deal to the arithmetically-challenged. But
if you can afford disposable synthetic ATF, you can probably afford to
self-insure...)

FWIW, my car's ATF seems to be ageing more slowly over the past 70K mi than it
did over the first 60K. So it would be unwise to examine the fluid at 25K mi
and come to the extrapolated conclusion that the ATF will never make it to 50K
mi.

But I strongly urge you to resist the temptation to over-maintain these ATs;
they were meant to be seen (and do best when treated) as a 'sealed' system (IOW,
they do best when simply left alone, hence Volvo's insane-sounding recommendation
to simply leave them alone).

Of course, to do so will mean resisting the advice of those who've been unable
to resist said temptation, which is tricky once you realize how the "pros" only
see the few that fail (a tiny percentage of these things ever have problems,
and only a small percentage of those have anything to do with ATF, and few of
those would have been any better off had they used synth ATF), but the power of
the internet magnifies these tiny minority bad experiences out of proportion.

If your AT is really chewing up its ATF, and your car is still under warranty,
it would not be in your interest to spend extra money to conceal the problem by
treating a symptom. In these cars, a bad transmission can cause the ATF to bake,
but failure to change the ATF is only responsible for transmission failure in
very rare circumstances (do you tow a 3000# trailer up hills very often?).

Too many of those giving advice believe in superstitious/profitable/gratuitous
ATF changes because they are more sure of the cost of a replacement transmission
than they are of the cause-effect relationship between failing ATs and failing
ATF.

Dexron is the most over-engineered fluid in your car. And in our cars, the ATF
just doesn't get worked very hard in anything even remotely resembling normal
use.

BTW, I'm on my 2nd turbo car. The last one had a nearly-identical Aisin-Warner
transmission. Each car always had Mobil One in the crankcase and std Dexron in
the AT. I now have over a quarter of a million not-always-sedate miles
accumulated over the 2 vehicles without any ATF-related (exhaust manifold
gasketing problems and blown head gasket on the prev car don't count...)
incidents.

Changing the ATF every other month and not having problems only proves that the
maintainer managed to not screw anything up. Going 70+K mi at a stretch using
std Dexron w/o any problems suggests that the over-maintainers probably fall into
one of the following categories: profit-hungry professional maintainers, or
superstitious worry-wart owners with too much time/money on their hands.

As long as your ATF isn't thick, dark, burnt-smelling (a hint of burnt smell is
normal; it's a nose-curling smell of which you should be wary), it is what it
should be. And as long as it isn't thick/dark/burnt, the AT really doesn't give
a ___t how bright cherry red the ATF is! Of all the properties of hydraulic
fluid (which is ATF's primary mission in life), color is not operationally
significant.

Back in the old days, before ATs had lockup torque converters (TCs) and thus
the ATF was constantly being chewed up the whole time the car was being driven,
the std/sane/proven recommendation was to replace the ATF every 2 years or so.
Decades later, ATF is *much* improved, and leads a relatively sheltered, rarely
barely stressed, existence.

It would be absurd to not leave the ATF in service for years at a time.

- Dave; '95 854T, 131K mi