The brief
This 7 Series came in shifting roughly, the kind of jolt between gears that tells you the automatic gearbox is unhappy, and the history was the giveaway, the fluid had never been changed because the car was sold as having lifetime transmission fluid. There's no such thing as fluid that lasts forever in a gearbox. The automatic transmission fluid lubricates, cools, and does the hydraulic work of every shift, and it degrades under the heat and friction of years of driving. As it ages it stops protecting the clutch packs and the valve body, so shifts get harsh, slow, or flarey, and left long enough the clutches burn and the box fails. Once it's got to harsh shifting, a fluid-and-filter change alone often isn't enough, the box needs opening up and the worn parts inside renewed, an overhaul.
The diagnosis
A diagnostic and a road test confirmed harsh, delayed shifts, and a look at the old fluid showed it dark and worn, well past its life. With the box opened up, the valve body and the worn internal parts, seals and clutch components were the cause of the rough shifting, the result of running so long on tired fluid. That's a full gearbox overhaul, the valve body refurbished and the worn parts renewed, plus fresh ATF and a new filter, rather than a fluid change that wouldn't fix worn hardware.
The work
The gearbox was removed and stripped down, every part cleaned thoroughly, and the worn clutch components, seals and the valve body refurbished or renewed as needed, all to BMW spec. The box was reassembled with care, refitted to the car, and filled with the correct BMW ATF to the right level at the right temperature, the way the box wants it. The adaptations were reset so it relearns its shift points on fresh fluid and clean hardware. A road test confirmed smooth, prompt shifts up and down, no flare and no jolt, and the box behaving like it should.
The outcome
Smooth, prompt shifts through the whole range, no jolt between gears, no flare, fresh ATF and a clean filter, and a gearbox that drives like it's been looked after. The 7 Series went home with the box overhauled and shifting properly. Neglected transmission fluid is what gets a gearbox into this state, so the overhaul plus fresh ATF on a schedule from here keeps it out of trouble, and changing the fluid every 60,000 km is far cheaper than another overhaul.