If I may be so bold as to suggest;
Just change out the inter-injector return lines and keep an eye on the rest. If any lines begin to fail they will begin to sweat fuel, not fail altogether and at once. I believe if you replace all those lines you are suggesting you`ll be doing more work than needs to be done. From what I`ve researched, the only lines that are a problem are the inter-injectors and possibly the fuel filler neck.

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300TD W124, Two VW TDI Passat Wagons,Cummins Ram 250, Kubota Tractor
23 cylinders sipping the sweet sauce of the soy bean