Recently had an intermittent air leak in the fuel line
Traced it to a plastic tee piece which feeds diesel to the heater ,replaced that with a brass one now ok
But while trying to figure out the problem had to use the lifter pump which was painful so I swapped out the primary filter for one with a push pump
This came with its own problems as a direct replacement unit has changed from bsp fittings to parallel fittings with copper washers
it was worth it ,difference is unbelievable after a few pumps fuel now shoots outof the bleed screw
Unit bosch with lift pump using Delphi technologies 296 filters £47 on line