There seem to be a lot of accordions coming in for repair at the moment. Perhaps it’s the cold weather ?
Lots of them are in for revalving. Their old leather valves have curled and stiffened, and in many cases the glue has failed and they’ve dropped off. These loose valves then have a tendency to find their way under pads and reed tongues. In the worst cases I’ve seen them jamming the bass mechanism.
Part of the problem is storage. Accordions should always be stored on their feet, as this leaves the valves hanging vertically. If an accordion is stored on its side, gravity pulls one set of valves open. Eventually they curl into the open position permanently, and they’ll need replacing. A full, or indeed partial, revalve on a large accordion can be an expensive and time consuming business.
There is also an argument to be made here against double cassotto arrangements with reeds arrayed in them. However you store such an instrument there will always be a set of valves which will have a tendency to curl over time. They do sound good though!