This may, or may not, add to the debate but I have just had my transmission rebuilt after the torque converter failed (lock up sprag clutch sheared) and caused catastophic damage due to debris in the oil damaging various clutches downstream and ruining the oil pump to the extent that metal shavings from the pump wrecked the gearset for 1st to 3rd too. The rebuild shop is a ZF specialist and they want the car back after 6months/6,000 miles to do a complete fluid and filter change. The original failure occurred at 42k miles.

More worryingly - and I pass on on for that reason - was his comment that they are now seeing so may of the 6-speed auto failures (not just in BMWs) they now keep the spares on site whereas they used to special order them. Most of the failures are actually being caused by electronics or electrically controlled hydraulic devices breaking rersulting in downstream failures when vavles operate incorrectly or fail to operate at all - and not fluid related.

__________________
Me:
Current: 2011 E71 40D Vermilion Red/Beige Nappa

Wifey:
Current: 2012 R80 Countryman SDX Green/Cream