So, the g.d. o-ring had slipped out of the receiving groove in the res on the back side where I couldn't see it. Must have happened while I carried the machine from the worktable to it's accustomed spot, because it wasn't leaking before.
So I put it back in as far as I could turn with fingers, then cranked it in with pliers, checking the o-ring every 1/4 turn. It's in there good now. Checked all my other barbs while the loop was dry, they look ok. BTW, all leaks I found were around barb threads, not from tubing. The Primochills seem to seal fine with zap straps.
We'll have to blame this one on operator error, unfortunately.
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