The line you have apart in the picture is the high pressure line, steel on steel, no rubber there. Take the tee off that goes across the top, that's where the rubber seals go, and that's what usually leaks. If you are positive that the steel on steel part you have open is leaking, then you could try tightening it up as tight as you dare. If you crack that, then you're still going to replace the line and injector, the injector will be easier to get than the line, so not much lost if you break something.