I did figured it out in the past, but don't think you really need the info for repairs.
What is a bit confusing that the prefilter and main filter are in the same housing, while the prime pump between takes 2 tubings. Than shut off valve has 2 stages. I assumed this is safety measure. Older diesels have manual levels for shutting off in emergency.
That makes for a small maze, what would not be a problem would the MB used the eyed ends like in the older designs, than the weak orings.