Thanks to you both for your insight.
I did not do a soapy water test before removing the injectors, so that evidentiary ship has sailed.
I will follow up again here when the injector shop gets back to me. It's this place, FWIW:
https://nwfuel.ca/I'm pretty sure the leak was in the joint between the two injector halves. It was wet with fuel in that seam, and below it, but totally dry above it. So it is unlikely to be a problem with the return nipples or the hard line feed. And I can't imagine how the fuel could leak up from the cylinder head to the injector seam, then do a 180* drop into the seam, all without leaving any wet traces above that seam. So I'm pretty sure that's the issue.
While dealing with this injector leak, I found a nice air bubble in the clear fuel feed line going to the injection pump, and I saw that the copper washers on the top & bottom of the banjo bolt there are wet.
So there is a second leak in the system, joy.
I cranked the banjo bolt a little tighter, maybe a twelfth of a turn, but without using a torque wrench I am reluctant to be too enthusiastic. Once the injectors are back in, I will see if there are still air bubbles in that feed line.
Anyone have the torque spec for that banjo bolt handy?
Am I best advised to replace the copper washers there, anyway?
One step at a time. Vehicles eat themselves. Entropy comes to us all.
Also, on removal of the hard lines, I noticed that all the vibration clamps were missing. God knows how long it ran that way. I see it's no picnic to find replacement AAZ hard lines these days, either. Joy.
NW Fuel Injection will do a hard line test at 300 bar, so that's double what the injectors are rated. I would rather the lines break on a shop bench than in the back of beyond.