@AccordionBruce @keys ah yes, I've removed the reed block that the linkage goes into, and there's a kind of shutter thing that shuts off all of the 16' reeds while the bar is pressed. Still no sign of any kind of ratchet or anything to hold it in that position.
The springs on the bass valves don't have enough spring to close them again when you release the button. Possibly a bit of lube would be enough to fix it, but since I'll have to dismantle the whole machine to do it, and I still won't be able to play the instrument even when it's working, it's going to the back of the queue. 