There should be two copper washers that go on each side of the banjo block. The sequence should be bango bolt hex head, copper washer, hose block, copper washer, and finally caliper body. Sometimes the aftermarket calipers come with washers in the box, and other times not. The old ones can be used if they are heated up cherry red then allowed to cool down, softening them so then can be crushed again. Otherwise they are too work hardened and you have to overtorque the bolt to seal them.