I took out the coolant from my car and poured it into clean cup, and compared to the fresh MB antifreeze mixture.
The coolant from my car was clean, but it had slightly green tint. After beeing agitated, the foam on top of the coolant from my car lasted long like soap water.

I went to the MB dealer who replaced radiator, thermostant and coolant this summer. Nothing was done to the cooling system since the service at that dealer.

Surprisingly, they said it was OK! I still see the foam on top of the coolant in the coolant reservoir. It can bee seen from outside. It can be seen by opening the reservoir cap. They said there was small amount of foam, but the car drived normally. They did nothing, and charged half hour diagnostic fee.

Shall I go to that dealer again, or shall I just flush coolant at other place?

__________________
1992 300D 2.5 turbo diesel. 319 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.