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.