GC inlet pressure rises slowly

I have a 6890B GC system.   The pressure in the inlet takes a long time to rise, and sometimes triggers an inlet shutdown.  I have plugged the column outlet, changed the gold seal, septum, liner, o-ring.   behavior doesn't change.  Interestingly, when i use pulsed splitless mode, the pressure rises very rapidly for the pressure pulse.   So this tells me i have plenty of pressure at the inlet and the (presumable) leak is in a location controlled by the pulsed splitless injection sequence.   Anyone have any idea what this is telling me?  

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