This is how I do the fluid Exchange method for the W210 and W140 which out of the 722.6 transmission the exit line is on the driver side, and the return on the passenger side.

On the older tranny's they both come out of one side..

The process is the same?

See post 11 for the W210

Will Vin# reveal Torque Converter Drain Plug - Mercedes-Benz Forum

See Post 6 For W140

What is my transmission? Fluid? - Mercedes-Benz Forum

For others with a first generation 722.6's (All mid to late 90's cars). I'd suggest you do not do this as you can wipe-clean the K2 bushing bearing clean of lubricant, and you may get K2 bearing failure. Second Generation 722.6's are okay(+2000)

Hope it helps,

Martin