Likely rocking horse poop Paul. The image I posted above of Boss one was from an auction site and historical sale. Very little other info on this brand on the net.
Sounds like you have the means of repairing yours though, and a well worth exercise by the sound
of it.
Having repaired many vintage horns over the years (although few air ones), I will add that thickness and material of horn diaphragm are critical to sound made, so you will need to experiment. The last one I worked on was a hunting horn with modern driver tested with low pressure air line.
