> and it have the mission of torque transmission through the torque converter.

True, but consider that that has traditionally been true of automatics through the decades. Back then, ATF was being chewed up in the torque converter virtually continuously. Back then Dexron was less durable than it is today, and, even then, ATF was easily good for 2 yrs / 24K miles. (IOW, change primitive old Dexron that frequently in primitive old automatic transmissions and they'd last 'forever').

Fast-forward to today:

Dexron is much more oxidation-resistant than in those days.

PLUS, with today's electronically-controlled transmissions, the torque converter remains 'locked' 99% (98%?) of the time. So the ATF only has "the mission of torque transmission through the torque converter" 1% or 2% of the time.

Thus, no matter how far-fetched it may sound, it is not at all out of the realm of possibility for modern ATF in a modern AT to be good for, say, 12 yrs / 240K miles. It really does lead a pampered life. Unless you drag race your car and/or do a lot of heavy towing and a lot of stop-and-go driving in extremely high temperatures, the ATF may well out-last the rest of the car. As such, I believe that letting the AT flush its own ATF with more Dexron every 70K - 100K mi or so is more than adqueate maintenance for all even-remotely-normal use patterns. The clutch material build-up that occurs in ATF over time is normal/natural, and expected by the AT's designers; the AT's 'brain' will compensate over time for the gradual change in the ATF's "grabbiness". (This is why you want to reset the AT's ECU after flushing the well-used Dexron with new.)

People who switch to synthetic ATF and then regularly change it are a (pseudo)terrorist's best pseudovictim: they worry too much, become afraid, behave irrationally (usually expensively so).

- Dave; '95 854T, 143K mi