It appears that the Banshee weapons for today do not have a masterwork slot. I am unsure to why this is, especially because Banshee weapons have had masterwork slots. My guess is a bug. I am not sure why this had to happen when Banshee is selling the God roll Truthteller, but we have to deal with it. If someone knows more information I would love to have someone shed some light on this. But, make sure to pick up the truthteller anyways, it is a fantastic roll for high end PVE.