Kyle, John 

Today we applied Apiezon Q putty to that portion of the leak region that we could access, i.e. 2" of seam weld+stitch weld behind the support gusset and 2" of seam weld+stitch weld on the opposite side of the stiffener ring (not blocked by the gusset).  Basically the known region of the leak site minus the inaccessible space between the stiffener ring and the spool wall -> No change in Y-mid pressure.  

Kyle

After lunch, I wet the entire region with Isopropyl alcohol -> no change -> Next, I removed the Apiezon Q putty using various scrapers and wire brushes and then used opposite facing wedges to compress a silicone rubber mat against a cut "feature" (that Gerardo had noticed yesterday which is just below the seam weld behind the support gusset and which is ~1.25" away from the stiffener ring) and the support stand.  The Y-mid pressure began to respond.  This cut had been covered by the putty and should have been sealed.

Kyle, Gerardo, John, Bubba 

We removed the silicone rubber mat but the pressure continued to drop -> We sprayed the entire area with Isopropyl alcohol and the pressure continued to drop -> We wet the region with Acetone and the pressure continued to drop -> We applied VACSEAL (SPI #5052-AB, Lot 1180402) to the cut and the pressure continued to drop 

CONCLUSION: 
It may be that the compressed rubber mat was more effective at getting remnants of the initial putty applied into the deep cut feature than was John and I's initial attempt using rigid flat tools.  Another possibility is that the brushes used to remove the putty may have embed putty more effectively into the leak.  Phase-change freezing of the initially applied alcohol is another possibility except that the leak stayed plugged for longer than the alcohol would have stayed frozen.  

At this point, I think that we can say that the leak is at the cut in the spool wall.  How permanently it stays plugged will be a function of the interaction of all of the substances which were applied to it.