The steel fuel lines on my 79 300SD (617 diesel 3.0L 5cyl.) have decided to begin leaking at the fitting. This began after the onset of our first really cold weather. I have tightened the worst offender (front cylinder) as much as I dare. This lessened the leak somewhat, but fuel still weeps from the area around the tubing where it passes through the fitting nut. All small rubber return hoses have been replaced, you can wipe the injector area clean and see the fuel leak from atop the fitting.

There is another steel line leaking to a lesser extent as well. I understand there is no seal to go bad, these are flare fittings. What can I do? Do these steel lines crack at the flare or something?

Thanks in advance for your help... Dave Larson