IMO, it's not enough to just drain/refill the gearbox oil. The filter needs to be changed and perhaps most importantly, the pan and the magnets need to be cleaned. A surprising amount of fine sludge accumulates on the bottom of the pan and around the magnets. Some argue that removing this friction clutch residue is what leads to failure after a trans oil change; I would suggest that changing the oil without removing this crud is what leads to early failure, as the new fluid/detergent dissolves some of it and then recirculates it.

I'm due for another trans oil service; my X5 has 154k miles (bought it new in Feb 01) and this will be the third time. Still shifts like butter. Of course, now that I've said that, it'll probably grenade itself tomorrow.

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12 E70 3.5i xDrive
03 E46 330i ZHP
01 E53 3.0i
98 E36 323is
12 Audi A4 Quattro
79 Triumph Spitfire
73 MGB