Rubber fuel hoses to main fuel lines in engine bay

Hi,

I have a vt v6, which hasn't been driven for a few months now. I have just done a full service, and when i started it up i noticed that there is a small fuel leak coming from the connection between the main fuel line and the rubber hose fitting. I have no idea how to undo this fitting as it is the round metal one on the line. Obviously i need to relieve the pressure from the lines first (still need to change the fuel filter anyway)

Could it just be that because it was sitting for so long it has started to leak?? I haven't noticed fuel leaking before this (only had the car for 6 months or so) Also the rubber hoses look like they have been replaced not too long ago.

Cant find anything on this fitting in the Gregory's or Holden manuals..

Any help would be much appreciated!