Hey Ken,
       First I will assume that you cleaned everything, including the inside
of the big nut and the threads, checked for nicks and gouges, and used a new
O-ring.  Next thing to look for is the tiny hairline cracks that can appear
just above the flared part, where the nut seats.  That is why I have recently
had to replace mine.
       I think that is where all the stresses of engine movement and
vibration are transferred to the hoses, right above the nut.  I got lucky and
found one at a junk yard that matched.

Bill Marshall
85 GL Tiico
Bradenton FL