Bosch injector pump problem

My Scania 112 seems to have an air leak in the fuel system. After sitting for a while it requires bleeding. Today I went to start it, tipped the cab and saw moisture under the nut on #2 line(THE ONE THAT RETAINS THE FUEL PIPE) on the injector pump again. Multiple times I have loosened this nut and tightened it. The fuel line from the tank including the pickup pipe into tank, to the lift pump have been replaced, all filters replaced, lift pump serviced. Where the fuel is leaking be the cause of air getting into the system?
Bosch inline pump. The numbers on the tag read

541 14587B
PE6 120A720 RS7001
0 402 646 801
Here is a head scratcher- The fuel return to tank line has a filter fitted!!!!!!!!!!!!

 

That pump, like most pumps are a closed system.. any leak will allow the pressure that is supposed to be in the pump to "fall off" & cause a hard start problem..
What are u TORQUEING the nut to?? & HOW are u torqueing it?? VISE GRIPS?? U GOTTA HAVE the special tool to tighten it properly..
There is an Oring on the holder.. & if I remember correctly, a copper gasket under it.. its either under the holder or under the delivery valve.. & they have 2 diff. torques..
Gasket on top of dvalve is 65ft lbs.. & gasket UNDER dvalve or no gasket at all{metal to metal seal} is 90ft lbs..
THATS not a head scratcher.. THATS just plain stupid..

 

I should have made the first post clearer. The leak appears to coming out from under the hex head fitting that retains the injector line to the nipple that needs the special tool.

 

So basically your line is leaking..?? Its not uncommon..
use some sand paper on the end.. the line could be split or the piece that it screws to could be split??