How to bleed the secondary fuel filter:
FSM job 07.1-140
Three different sizes of banjo bolts -> three different threads => can only be assembled one way.
Second diagram shows the routing of the fuel lines to the secondary fuel filter.
Mercedes-Benz Teilekatalog (Ersatzteile online)
You may need to replace the crush washers on the banjo fitttings.
Sometimes you can re-use them without getting an air leak.