Penny & Giles, eat your conductive plastic hearts out.
The tab at top is the cover lock; push it and turn to remove it for cleaning and service
…
Big silver contact studs lead to the resistors inside.
In normal service these would be lubricated with Daven oil. This is a total mystery to me — it’s been out of production for decades, and I have no idea what a proper substitute would be.
The only other place I’ve seen rotary switches this hardcore are in avionics.
The Daven step attenuator was used in older broadcast consoles — I’m not sure on the details but I’ve heard that WVUM had one.