I have the same issue with the vehicle starting, however mine is intermitant.

Diagnosis;
Car will stat sometimes ok, sometimes not or sumtimes run then stall.
Every morning for the last week I have stuck my head under the bonnet to check things before and after starting. On the days it wont start there is a bubble of air in the diesel fuel line just after what i believe is the fuel pump (but im uinsure what is is really, its jsut a little black block at the the top front of the engine that is directly after the water filter and directly before the injectors by way of fuel line.)
On days it starts fine there is no air bubble at all.
Yes these lines are connected by a simple O ring and clip, however I have to wait a week to get parts from mercedies as the mechanic does not want to replace the O ring without the complete part as the clip is so brittle from the engine heat.