New washers and spill rail fitted 6 months agoJust try some new washers, they go hard over time.
The dowty seals seal on the outside face as the rubber bit is proud of the steel washer, I use them all the time on sump plugs.I don't think that'll work, the sealing area is on the outside edge of the copper gasket, not the inner edge like a Dowty seal. I don't recall ever seeing them on fuel systems -Renault use them on sump plugs so there must be some hydrocarbon resistant versions - I just don't think it'll stop your leaks, you probably need new banjo unions.
I'm aware of the inferior type, these were "non magnetic"Are you sure the washers are copper, its not unknown for the cheaper ones to be steel plated in copper.
Banjo seals are standard fit on scania sump plugs.I use them some of the time on sump plugs The difference is that a sump plug & sump have reasonably flat and wide surfaces from the thread so the flexible part is compressed before the metal part stops movement and takes the torque to hold it in place, a banjo isn't tight to the thread and has little 'land' for the soft part of the seal to seal on. Unless there is seal and metal able to be compressed under the edge of the banjo, then it either won't seal, or will fail as the torque is not able to be maintained due to the metal part of the washer not being under compression.