Thanks for your observation, Shannon. This helps. I won’t just start removing all the keys. At first it seemed to me that the plunger shaft screws directly into the bottom of the key, but now it looks, upon closer inspection, as though there is a little disk (like a nail head) at the top of the shaft that slides into position in a receptacle on the bottom of the key, so that when the key spring is removed, the key shaft can be freed from the key, after which I suppose the plunger may be removable from the other end. It may be more complicated than that, but the best approach is probably to remove one or two keys and see.