I'd go for a binary chop and insert a few ball valves in the line
to isolate parts of the system. At least you'll be able to better
pinpoint what parts to check. Turn off half the system overnight
and see if it still leaks.

Bob Engelhardt wrote:

Now it has become a challenge. I've GOT to find that leak! Before I
start taking parts off to eliminate them as leaks, does anybody have any
tips/tricks for finding leaks that might save me the work?