[700rpm]

I doubt the horn is dead, probably just sleeping. Crosscut has good suggestions. I would only add before you do anything just back the adjusting screw off two or three clicks, then push the button. That might be enough. If it struggles, then give it nudge with your finger and otherwise follow Crosscut’s advice.

Also, there are Model A clubs all over the world. If you put your location in your sign in profile we might be able to suggest one for you, and I can guarantee they would want to help you.
Let us know what happens.