I did the work last weekend and thought I'd share results, FWIW.
Drained out under 5L of fluid, which looked pretty good to me. I have an 07 with <30K miles.
I replaced the mechatronic adapter sleeve because I had a leak. I also replaced the mechatronic adapter seal, which requires you to drop the mechatronic assembly then carefully retorque it in place. All reasonably priced torque wrenches I could find were inaccurate at 8Nm, so I did it by hand. Not recommended, but far better than using a Harbor Freight torque wrench.
Refilled with ~4.8L of Pentosin ATF-1. I'll probably support the car at an angle and try to get a bit more in.
Reset transmission adaptations using BT scan tool.
Results: Initially the slip in lower gears was better, but still there. I was bummed. A few days of driving and it is nearly gone, if not back to the way it always was. I can't really call it slip because under load the tranny does not slip at all, none, never, and I'm FBO with meth and JB4. I would characterize it as late shifting that allows a slight RPM blip between shifts.
Whatever happened, the problem is resolved. My recommendation to others experiencing this would be to just do the fluid change, replace the sleeve because they leak, but don't drop the mechatronic and do the other seal. I suspect that replacing half of the fluid (about all we can get out, that isn't in the torque converter) and filling to proper level will address the problem.
I'm pretty disgusted by a <30K mile transmission having any problems whatsoever. GM and Ford have been making flawless AT for decades, so it's the last point of failure I'd expect on a BMW. I'm hoping this was more of a software issue, and will look more into that, but strange that a fluid change would address it.