Mudman, underexposure at higher ISO is where we see the vertical line problem the easiest. You should also see it in dark/shadow areas at lower ISO if you pixel-peep closely. This is a problem that you should raise with the seller of your camera.
Not an unusual problem, and some have suggested it will be an on-going one with any digital, caused over time by cosmic ray strikes on the sensor. It may be seen as a line or just one or more hot/dead pixels. Leica will fix this (should be no charge) probably by mapping out the affected pixel(s).
Best to address this issue sooner than later.
In the meantime, you probably have a bunch of pics that will show the line under close examination. A way to eliminate the line that has worked well for me: Output DNG to full-size TIFF. Locate the line. Select everything to the right of the line and hit the left-arrow key to move the selection one pixel to the left. There, line gone! On to the next pic.