Friday I had improved by a factor of 2x or so the persistent air leak in the Vertex RGA by torquing the suspect "factory" flange between the analyzer and it's protective nipple.  This leak turned out to be only a small fraction of the total leak rate observed, i.e. there was more than one leak.  Today I again removed all of the heat tapes and aluminum foil to gain access to the CF joints for additional helium leak testing.  Note that all joints had been tested individually at various times prior to this most recent bake exercise as well as collectively via bagging the complete RGA assembly.  Again, the joints tested good today so I decided to do a "fire hose" test and upped the flow of helium to "audible" values.  John W. was physically present this time and his well documented aura was in full effect so we immediately found that the turbo vent valve was the culprit.  This is consistent with all of the previous observations as the Turbo vent valve had not been sprayed in earlier hunts, the reasoning being that it is an O-ring seal with a very small cross section and permeates to the point of being a nuisance when leak hunting (normally!).  Also, the rate at which is was leaking was just smaller than that which would show up on the foreline pressure gauge but just big enough for the portion that reverse flowed through the turbo stages could account for the value of observed leaking at the turbo inlet - Arrgghh!!!!! 

I took scans and decoupled the turbo and pump carts and shut all noise sources off.  

I'll make an entry tomorrow with the scan data.