Ron's story on the horn is exactly like mine. Try as you might - it's a hopeless cause to replace these horns.
I am on my third Grady. All of them have those crap Ongaro (sp.) dual electric horns. All have failed. And frankly, the horn isn't all that loud either. I remember replacing one on my 265 way back when. In one season, it was toast.
So - I - like Ron - simply carry a hand held air horn to get me past a USCG inspection.
I thought about paying big bucks ( like $300-$500) for a really high quality, dual trumpet, SS air horn and mount it on the front starboard side of my hard top. Then I sat down and said forget it! The simple hand held air horn won out. In five plus years of use, I can't recall ever regretting this decision (I do my boating 99% in the open ocean).
Gradys are good boats, but those electric Ongaro air horns are crap.