I had the EXACT problem about 2 weeks ago. The Feed and Return line from the tank go along the drivers side and directly in front of the rear wheel they turn up toward the tank. They rust out at that bend from being sprayed by the wheel and because the bends are weaker. Your idea of rubber lines is exactly what I did. Chopped both lines in front of the leak and at a convenient place behind the leak. Make sure to get 5/16 fuel line that can carry diesel (If they don't have it ask for trans cooler line, that's what I use, Diesel won't eat it). I would get more then a few feet. Although the leak is most likely small you may find the rust as spread over several feet of line and only broken through at one point.

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Serenity-86' 300SDL 482,000 miles (on a "14" head!)