Update...
All is well! Everything works as it should. The $50 used part had a LOT more 'springiness' in the horn pad.
In a moment of malt-barley-beverage-fueled madness, I decided to risk opening the old one up...curiosity killed the cat, right??? Fortunately, there were no explosions, and I discovered what actually makes the horn work! There's a membrane switch in there about the same shape as a football, and about half the size. It was completely flat, no tactile response, no 'spring-back' as there should be (I've dealt with plenty of equipment that uses membrane switches, and they're like pushing on a stiff bubble that wants to be a bubble!).
Factory part was $830. Saved a buck or two...now, it's just about finding a flat spot in the desert to 'dispose' of the old one...maybe see how high I can launch (insert object here!).
Cheers!