Carryover/Ghost peak in GC 7890B


I am having trouble with carryover peaks in baseline in my 7890B GC with micro-ECD detector. To be specific, the baseline shows kind of a s-shaped just right before our peak of interest begins to appear which interferes with the peak shape.

A little background story, we had problems with our nitrogen generators and damaged some GCs. Since then we have worked with nitrogen cylinders and we have a 7890A GC with micro-ECD that is working perfectly. However, our 7890B GC has been giving problems since then, even though (we think) we have done everything.

We have changed the gas lines, column, gold seal, micro liner, syringe, filters, and have done several test to see where the contamination might be coming from and everything from the inlet to the detector have come out good and clean. We noticed too that if we run pure ethanol, the carryover doesn't come out, but when we run blank (40%v/v ethanol) the carryover comes back. We have tried different blank samples with different source of water and they came out the same. I don't know what else to do, initially we though the contamination came from the detector, but we have done several bake-outs and the signal is relatively good (200-300) and have done condensation tests and the carryover doesn't appear. 

Thanks in advance.

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