Leak is either from the DV or the hard fuel line right above it. Sometimes you have to just take it apart and closely examine the seals and joints to figure it out. Have you tried just putting a wrench on it and tightening things up just a bit? Would be nice to find out that it simply has gotten a bit loose with time.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC