I thought it made sense to put this in a separate thread from the regular oil analysis. Anyway I did my first transmission fluid change (3 drain/fill sessions a week apart) starting around 71,200 miles. During the first, I captured a sample and sent it away for analysis. And before you ask, yes...
The fluid is only half of the answer. The other half of the answer, is the transmission. Noone truly knows how tolerant the SA transmission is of fluid spec changes. An example is some of the guns I work on.
Some of the M4 type rifles I mess with have properly sized gas ports for use with and without a suppressor. On those guns, if the gas tube and gas block and carrier gas key are not within spec, you WILL have malfunctions. On others, the manufacturer oversizes the gas port so that people can run trash ammo through them, without a suppressor, and the rifle will function with gusto no-matter what, to reduce warranty calls from the masses. These guns, I have used measured out of spec gas tubes, etc. on and they run absolutely fine.
So...is the SkyActiv a product with a narrow tolerance for fluid spec, or is it more like the latter example, where viscosity really isn't a huge player in the function of the transmission, comparatively, etc? I truly don't think anyone outside of Japan could answer that.