Just wanted to warn people before reading this as it (may) contain a slight quest spoiler.
As the topic may suggest, Ruined Overseers are nowhere to be found. They are required for "Old Rachival: Enginering a Disaster (Part 2)" (ie Winter Vale Engineer quests). I have been all over the place and had the pleasure of a dragon help me search for them and they are nowhere to be found.
As a side note, the Blighted Spanners drop, but would be nice if they stacked.