Refer to D:02:01 Note 10 for torque specs for the fuel lines. These are for use with new copper seals. If the joint should leak check for scoring, unevenness or dirt. Certainly the lines should not be under additional stress by having been twisted, bent or kinked. Another reason a joint can leak is, when assembling it, you accidentally miss a copper seal or use more than 1 per side. It doesn't take much additional torque to break the banjo (hollow) bolts so don't overtighten them to stop a leak. Leaks are hard to miss, you can smell them, even if you can't see them. A tiny leak at these pressures and the fuel will atomize and not always be visible. There can be NO leaks. While a leak can cause hard hot restart problems it should not cause a hard cold start problem. Recheck that you have the lines correctly connected and routed.