Mercedes-Benz 725.0 (9G-Tronic)

Mercedes-Benz's nine-speed torque-converter automatic — across almost the whole range since 2013, and, bought in, behind the Nissan Navara.

A great deal of what is reported as a fault is the ratio count. Nine ratios in a car driven gently means the transmission changes very often and hunts between the tall gears on a light throttle. That is behaviour rather than failure, and no amount of adaptation resets it away — a road test against another example of the same model is worth more here than a scan.

Its own recurring theme is fluid, and the marketing is against you. These units are presented as filled for life, and they are not: torque converter lock-up shudder — a fine vibration at low speed under light load, easily mistaken for a misfire or a wheel balance — is the standard first symptom of fluid that has aged, and it is far cheaper to address at that stage than after.

It is not the 722.9. The seven-speed it replaced has a different valve body, different failure modes and a very well-known conductor-plate fault; none of that transfers, and a search that does not distinguish the two returns mostly the older unit because it has been on the road far longer.