Yes, I have been spraying all connections insescently with star san, even dunking ones that I can into a container of star san. I just can't find any leaks.
Here is what I have done briefly.
I first checked the primary regulator. Sprayed the connection between the tank and regulator. No bubbles. Charged up the regulator noted where the needles where on the gauges and shut off the CO2 bottle. Left it for about a day. No drop in pressure.
The line going out of the primary regulator is a short hose connected with a swivel hose barb and it travels to a T junction with 2 shutoff valves. I sprayed the connection coming out of the primary with star san with the CO2 open. No bubbles. I then dunked the T connection with the shut-off valves turned off. No bubbles.
One shut-off goes directly to a barbed swivel attached to a flare fitting QD. I opened that valve and dunked the QD in star san. No bubbles. Shut the valve.
The other side of the T goes to a bank of 3 secondary regulators. I turned the pressure control screws all the way open so no pressure was going out of the regulators and opened the valve at the T. I sprayed the barb fitting going in to the regulators, the fittings between the regs, and the end plug. No bubbles.
The first 2 regulators in the series are each connected to a two way manifold inside the kegerator. The third reg. goes directly to a barb swivel and flared QD. I shut all the manifold valves off and had the QD not connected to a keg. I then pressurized one reg. at a time, noted the pressure, and turned off the gas back at the T. I come back in about 8 hours and... The pressure has dropped. I repeat the process with each regulator individually. Same deal.
I replaced all the hoses going in to the regulator bank and traveling to the manifolds and QD with new 3/16" beverage tubing and checked them again. Still had a pressure drop. If left long enough it would drop all the way to 0 by the way.
So? Is it the regulators? Can anything be done? Am I missing something to check?