Fuel leak from filler/pump

[framerateuk]

I've had a fuel leak for quite some time now, I've changed the whole fuel filler assembly (both the flexi and the actual cap) and I've replaced the overflow.

I didn't use any type of sealant beyond the clips provided, but I've bought a new fuel pump gasket and I noticed when googling that someone mentioned using a fuel resistant sealant (Hylomar). Now, when I disassembled the original filler, there was no sign of any sealent, but am I going wrong somewhere by not using it?

I've picked up some to use with the new pump gasket, but should I be using it on the filler neck and tank joints too?

(Car is an '09 Sigma - so pump sits into the top of the tank on the passenger side)