Yes, it's best to put a washer between the head of the banjo bolt and one between the line and caliper. I have reused washers and I guess I was lucky that I didn't get a lead because the washers collapse when the bolt is tightened. Some calipers have rings cut around the opening and this embosses into the copper ring. If the rings of the old washer and the caliper don't match up perfectly, you could have a path for a fluid leak. Use copper washers if available, instead of aluminum washers.