The fuel line at the tank is sometimes not replaced often enough ,these get hardened and sometimes leak with their age ,sepping air or leaking.The tank screen if not mentioned above could be another.Any lines blown out for safe measure while its opened up would be another quick and easy step to eliminate the questions.Kinked line if someone else has worked on the car in the past, people send jacks underneath these cars without looking for lines first , tire shops are the 1st ones to watch .It can be easy when looking at fueling issues if you start first with the tank ,start here and then work forward would be my advice ,this if all your filters have been changed and the primer pump is not leaking and a newer one has been installed .Diesels tend to not have nearly the problems as gas MBs come up with as they age ,you should find a remedy soon .Not a veggie car will be the last reveal,if the tank line is replaced youll have some evidence of veggie .Veggie cars will have a scent from the tank ,aroma is deep fried for sure.
Ill throw some hail marys to lookout for -banjo bolt cleaned ,always the first item ,brakes , trannie fluid ,filter , torq converter ,excessive carbon build up in intake and or exhaust pipe .ALL forward moving reducers if not functioning or filled properly.