Prior to venting, I sprayed helium around the welds which join the thin-wall MC tube to the thick flanges.  The LD background was 3.5 x 10-9 torr*L/sec -> no responses.  I did not spray all of the welds on the MC nozzles, roll seams or roll butt joints, however.  

Also, PT120A wasn't working today.  I think that I had drug my fall protection tether across the gauge pair the other day during leak testing and must have interrupted the cable connection.  I eventually had to remove and re-installed its cable to get it going which fixed it.