Being a diesel fuel shop mechanic, I have dealt with many of these problems on MB's and VW's.
Most car owners do not purchase the correct hose. We have the metric braided hose that you need to correctly fix the problem.
In rare cases, the "pressed" in fuel return pipe on the injector is causing the leak, but will leak again soon after the car is driven.
Most likely, the "wrong" fuel hose is used and it inflates after it is heated so long.
1987 300TDT 165K MILES