We replaced all three of them on the 77 240D. There was a parts mixup trying to order the return line from the pump to the fuel filter, and once we realized that the two lower lines were so cheap (I think one was $10, the other around $15) we just replaced all three. I don't think it needed to be done, but the parts were already in hand and it was cheap, so why not?
The clear plastic won't stay clear for long, but the new stuff was considerably less brittle than the old, and after 30 years it just seemed like a good idea.

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1971 280 SEL
1981 Volvo 242Tic | 1980 Bertone Coupe