Double07, thanks. While it at first it may seem unlikely there could be an oil filled unit, I was mindful of oil immersed transformer windings which have stood the test of time. It also would have allowed lubrication of far fewer parts. Dash-pots (if that term is allowed for oil as well as air) are historically prone to leakage, so I'm surprised at the added complexity.
I used to reach with my hat to test the vanes and was impressed with the exquisite smoothness of the rotation.
I'd imagine opening one of these units would be akin to working on a watch. I wonder if in the history of their manufacture, it was fully realised by the technicians just how critical the output data was. I recall one of our fleet of six BAC 1-11's used to have the igniters, come at a noticeably lower airspeed than the other five. It was the first indication of AoA being too high. Shake and then Push coming next. Always hand flying to ToC it was sometimes difficult in that aircraft when hot and heavy.