I had a leak in my kegerator CO2 system that was coming from the shutoff valve of my regulator. I have one of the 2-headed regulators so I can carb one keg and serve another keg each at their respective pressures. I found the leak to be in what looked like an improbable place - but upon inspection, it made sense. The MFL or barbed interface on a shut-off valve is an insert into the housing that contains the valve and screws into the regulator. Mine was loose. Had I figured this out *before* I replaced the valve entirely, I might have been able to save myself $12 for a new part and months of headaches. Maybe this can help someone else. Leak not in the line connection? Try tightening the valve insert.