Yesterday my mechanic replaced the corroded oil line no. 2 at the radiator with a new one.

I also decided to buy an original Mercedes oil change kit for the 5G-TRONIC 722.6 automatic gearbox, i.e.:
MB 236.14 oil,
gasket under the pan,
oil filter,
drain plug gasket,
plug.
It turned out that the old gearbox oil filter had the year 2004 written on it, which means that the oil in this gearbox had not been changed since new, i.e. for 21 years...

At the same time, the oil in the rear axle (differential) was also changed: Motul SAE 75W-85.

This car repair cost me $500.