Continual Fuel Line Leaks - Help Needed
 

I am experiencing fuel leaks at the point where the fuel pipe connects to the injection pump outlet port. This has happened to various cylinders occurring on 2 different cars I own: 1987 300TD and 1986 300SDL. My fuel pipes are secured in the plastic loom clips so vibration doesn't seem to be a problem. Occasionally the fuel pipe actually breaks right inside the ferrel nut. However several times there appears to be no problem whatsoever with the pipe, the ferrel or the seat in the pump outlet. No marks or signs of misalignment or debris???
Seems like a leak occurs and pipe needs replacing every few months. Any thoughts or experiences with this problem?

Thank you!