The outside front pipe- I think it is the low pressure return pipe- was leaking where it screws into the housing. I nipped it up, but it still oozes a bit. In the workshop manual it shows that the male part screws in flush and with a copper washer. Mine looks different. In does not screw in totally. I assume it works on a taper system.
Does anybody know whether this system has a O- ring seal or do I just add a small amount of PTFE tape to the thread. As it is a pressurized system, unlikely that any will ingress. My concern though is that it will be dissolved by the diesel.. Any insights will be appreciated.

The filter housings are known to become porous over time.

Mine is tight flush to the copper ring and fitting.

Cheers