I have a Style W Orchestrelle and found that the valve adjustment shaft
came loose.  These are accessed by going to the rear of the instrument
and opening the hooks on the sub-bass chest located to the right of the
mid portion (back of instrument).  This takes no more than 10 minutes.

If it's not in this unit you have a major problem!  Individual sound
registers have millions(!) of screws to gain access.

Greg Filardo