[Tx Firefighter]

Check the mating surfaces on the hose fitting for burrs. You might need to take a file and surface it a bit to make sure it is flat for the washers to bear against.

Use only copper crush washers. There is not a car made with plastic banjo bolt washers used in the brakes and there is a reason why. You simply cannot risk a plastic or fibre washer failing in this application. Copper only.