I have one similar to yours and what you have is complete but as you already know, the brass gear has become loose from
the pin.
View attachment 730017
On the left side is the small end of the "brass" gear with the other end being the larger part that connects to the other gears below.
You need to apply the JB Weld to the inside of the brass gear which means you have to disassemble the parts.
The long pin which runs through the brass gear from one end of the horn to the other end
has been installed with small rivets.
If you are able to remove the rivets to disassemble the pin from the gear to apply the JB Weld where it needs it
the most, then put it back...you won't have no problem. I'm not too knowledgeable with riveting.
The reason you need to apply the JB inside the gear is because of the constant force when you punch on the lever
to make the "sound".
Applying on the outside of the brass gear will only hold it in place for a short duration.
Did you know that the horn was not working before you bought it?