[glend (Glen)]

I have a problem with a hot 'artifact' area on the lower edge of my sensor somehow making it through the 'cosmetics' on DSS and appearing in the final stacked image.
I thought I had this solved on my first series of narrowband test images but since shifting to a new target last night it has reappeared. Here are the details: Mono Canon 450D (Cooled), with a couple of sensor faults which I have been able to process out with dithering and DSS cosmetics when shooting with my long focal length RC08 on Eta Carinea, but which reappears when shooting the Lagoon Nebula on the wider field Skywatcher MN190. I don't think I changed any of the DSS settings but maybe I did. Field of view signal area is different, on the RC08 there is data in the 'Hot' area, but on the Lagoon, there is the black of space with a couple of stars - if this makes any difference on cosmetic processing. The dithering and cosmetic processing in DSS does remove the bad row, and the column spike above the hot spot in both my test images on different scopes.
I have attached three files from last night, excuse the quality but they had to be downsized to post here, the first is a jpg of my Master Dark (a stack of darks shot at ISO1600 at 0C), the second jpg is a single 360" sub (ISO1600 at 0C) of my Lagoon session with the MN190, showing the artifacts I have to deal with; the third jpg is taken from the final stack TIFF produced by DSS. That final stacked Light from that session (10 were stacked) still show the Hot spot at the bottom.
What have I done wrong.
The final image is the same camera test shot stack on Eta C showing how the artifacts were previously processed out, using the same Master Dark, Master Offset.