0.001" per 8" is within spec. If you want to fiddle some more then you need to check if it's the column or the spindle, it's probably a bit of both. You can possibly adjust the spindle, if it's leaning forward (which is the most likely), by adjusting (tightening) the Z axis gib. A slight lean forward is possibly a good thing anyway as it will tend to be corrected when the machine is under load.
Just some thoughts and opinions.