Today I "meticulously" helium leak tested the Vertex RGA and couldn't find any external air leaks.  This is unfortunate as it now confirms the worst case which is that the suspect calibration gases are the likely source of our contaminates (including air).  

Some history -> After the initial bake out of this RGA, The scans seemed typical until exposed to the calibration gas(es) (see https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=27100 and https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=27078) after which, they looked dirty.  Hoping to still utilize these already installed leaks, I did a second bake (nominal 200C) only, this time, with both leak's isolation valves open and heated to 100C for the entire hot "soak" period before then being isolated - just prior to the temperature ramp down phase.  Following this second bake I had a new problem - I couldn't get anything but a "flat line" trace on the RGA, as if the ionizer was working but the mass filter (RF) section wasn't.  In addition to the standard "tapping" of the hardware, I opened the Kr cal-gas to get a burst and to confirm the symptom.  I eventually discovered that a small piece of aluminum foil was shorting out some pins in the RGA's electronics socket.  Once removed, the RGA worked fine with the exception that the scans looked "dirty" and had the presence of air.  What would they have looked like had I fixed the problem before exposing the baked RGA to the Kr? 

I now feel that these NOS calibration gases installed at the end-stations and now at the Vertex ought to be removed, discarded and replaced with proven "clean" ones.  To this end, I plan on temporarily installing their replacements (and the to-be-installed ones slated for the mid-station RGAs) on one of the VBOs to take a look at them before they get installed on the site RGAs.