Did you make any changes in your gas side between the last time used (without leak) and when you discovered you had a leak?? Anytime I make a change to the CO2 side of my kegging setup, I check those changes for leaks.
I actually cut the length on my gas lines down today (didn't need them as long anymore). Before I open up the manifold lines, I'm testing each of the lines I altered. Ended up needing to replace the plastic/nylon flare items that are used when you have metal on metal contact. The old ones were REALLY compressed and were not doing much at all. Just have the second body testing the line coming off of it (turned off the shutoff valve on the other one after confirming it's good). If that one is holding, I'll be able to open up all the valves in the system again.
Yes, the testing takes time. BUT, would you rather take some more time to confirm things are good (or correct them when you find they are not) or dump the CO2 out of your tank due to a leak you could have found and eliminated?