PropellerHead,
Thank you! I wanted to post a quick note back. Using a bunch of what you posted as motivation and tips my X (2005 x4.8is) is shifting better than I ever knew it could. While I would not have outright said before this that I had a broken transmission but it was clearly not performing as designed and had started to lag more in recent months.
No more kicking when shifting from 1st to 2nd. No more hanging in 2nd and 3rd and overall more consistent shifting overall. As a result my driving has is now more spirited. Not crazy but enough so that I'm also shocked for my mileage to have also increased. Yes, no kidding 5% or so. Clearly it was hanging in the lower gears more than I realized.
I have had good success with recent steps I took of swapping trans fluid and the parts plastic sealing parts between valve body and trans. All of the plastic tubes were shorter from age 1-2mm. The theory here is high pressure fluid leaks between valve body and trans due to these $20 in plastic parts shrinking. No special tools other than to drop trans pan. Valve body unbolts and drops even easier.
My Medtronic seal had a very slight leak too. I also think my overall fluid was low too as it took 7 liters to refill first time and second fluid swap only took 5.5 liters.
Trans oil change 7 liters life guard6 (bav auto)
dropped pan,
new filter (BMW parts counter)
dropped valve body
New metatronic seal (round electrics plug seal)
valve body seal , 4 tubes within trans (BMW)
took 2 liters into pan with engine off,
took 5 more with engine running, gear shift and 42C
Reset trans adaptations
Trans shifting much better now
Drove a 2 thousand miles and then for good measure changed trans filter and pan gasket 2nd time. Added fluid Zf lifeguard 6, took 5.5 liters at temp 40c
Trans resets adaptations again due to new fluid. If I were recommending to someone else I would not recommend 2nd pan drop but I would do 2nd fluid change.
Drives much better now. Shifting smooth and quick like I expect from a 2.5 ton sport truck.
Here are some other research links I complied looking into this.
Zf site directions
http://www.zf.com/na/content/media/u...28_Catalog.pdf
Zf lifeguard 6 fluid per zf site
Amazon $23
Bav auto $23 / liter
Welcome to bavauto.com | ZF Lifeguard 6 fluid - for 6-speed automatic transmissions
More on our trans
Everything about your ZF 6HP26 transmission issues | BMW Logic7 site
6hp26 tear down and history
Post 6 here shows the 5 seals (1 rectangle and 4 round tubes) valve body and trans plates
ZF 6HP26 Teardown