The Mercedes 5 speed 722.6 automatic (5G-Tronic / NAG1) has three faults that also recur on the used market: (1) the control electronics sit inside the gearbox housing, and a leaking connector lets oil onto the electronics; (2) cooling faults around 2003 (and later) can let antifreeze into the ATF, which shortens its life; (3) wear of the torque converter lock-up clutch contaminates the valve body and causes jerky shifts.
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The early cars (1995 to 2001) had planetary gear and freewheel wear; after 1998 to 2001 the design improved, and on the used market the W203/W211/W220 era is the typical find.
between 120,000 and 250,000 km
What to check
- Try it cold and warm: jerking or delayed shifts are suspect
- Look at the colour and smell of the ATF: burnt oil points to wear, and a "milky" emulsion means antifreeze in the ATF
- Ask for a fault code read on the gearbox controller
