The rear column on my 7890B is not holding pressure. I have removed the column and plugged the inlet (where the column nut fits) with a plug nut (#21883), checked the nut that covers the septum for tightness, and the housing portion that enters the oven and encases the gold seal for tightness. Still no pressure increase. I moved the carrier gas weldment that normally feeds into the front port to the rear. It is not holding pressure. However, I don’t know at what point the GC actually measures the injection port pressure, so I’m unsure whether this means the weldment is cracked or the problem lies elsewhere. Can you please help me interpret this result?