there are one or in some cars two vent lines with open ends, They go to the atmosphere to vent some device on the engine and the theory MB had was to pull air from inside the car rather than under the hood where its probably dirty. The vent lines are always black.
There are two lines that go (went) to the yellow one way (check) valve and drive the CLS (central locking system) and control pods for the A/C. You may need to find a similar car and do an eyeball comparison.
Now you know one reason some JiffyLubes mandated a NO MERCEDES DIESEL policy! they mucked up more than few cars and their insurance bought some new engines after the owners drove out and lost all the oil due to something the oil changer tech did wrong
Your back is probably real tired from replacing the stand gasket, so just try some vac lines and see if you get it right, its the transmission vac line that some people accidentally yank loose (then you have neck wrenching shifts)