IMHO, the most critical line and arguably the most suceptible to corrosion is the connecting line between the two front brakes. First because about 65% of your stopping force comes from the two front brakes and a leak or blow-out will rob you of that much stopping force, and second- because the line in question runs behind the battery up in the front trunk and is poorly protected (by only a loose piece of shrink tubing).
THe job is complicated a bit by the stock tubing being metric so it does not fit U.S- made flairing tools. Wrapping the tube with a piece of shim stock allows it to fit without slipping. Cut up a beer can for the shim stock.