Pumped for 4-5 hours today.  The time it takes to build up a positive pressure (following cracking the tube fitting and equalizing to room pressure) seems to have decreased slightly from yesterday - I should probably start recording the times and take notes!  Curiously, if I don't relief the accumulated gas by cracking the tube fitting, the pressure build up is partially reversible - meaning, if let alone, it can fluctuate between higher then lower positive values.  

Anyway, this exercise is probably worth continuing as it isn't making things worse and it almost seems to be behaving more like a poor conductance than a complete blockage now.  Of course, even if we are removing the obstructing material, it could take "a very long time" using this method!  

I am leaving the sensing line connected to the UHP N2 line (set at 0.4 LPM @ 15 psi).