I would drain the loop and pull that part and disassemble and inspect closely. Could be an O-ring defect or a milling defect or it could be that it just needs a little hair of Delrin removed that is allowing water to wick past the ring.
I had some mysterious issues with a DDC Dual top/Res combo a while back and found that there were tiny hairs of delrin trapped under the O ring and they acted like wicks that would conduct the fluid out past the O ring. Pulled those off and it was water tight.
Delrin is tough and chewy and if the milling tools are not sharp enough they will leave all sorts of stuff like that behind in the cut path.
This is a zombie thread. I have been running with no problems for almost three months now. The problem just went away.
Thanks for the info though. It could most easily help me in the future.