Maine, it was transferring starsan keg to keg. I tend to leave out details, sorry
Tom, It was leaking above the clamp at the end of the cut tubing where the tubing meets the swivel nut.
I have other similar lines that never leaked. This I made up from spare parts. I tried replacing the QD, replacing swivel nuts, replacing barbs, replacing clamps, with the nylon washer & without. I keep about a half dozen spare barbs & swivel nuts in a plastic snap lid container. They are all the same size, but likely came from different sources. Maybe you need to keep the original barb & original nut as a mated pair? This morning I must have finally hit the right combo. Transferred at 10 psi without a drop.
Thank you.