Save the fittings that are on the end of the line now and reuse them.
Get some 6mm line, 2 flare nuts and a matching union. The place you order the line and fittings from can make sure the nuts and the union match. As long as you don't damage the fitting as you remove it from the reservoir, you can bubble flare it on to the new spiced line.
When I damaged a flare nut, the only solution for me was to mail it to the place I ordered the lines from and have them match it. It pays to be very careful in the first place.
