Can anyone offer a repair procedure or guide to restoring a non-functioning horn?

We have two original horns. One worked fine when wired to a car battery. The other is silent. Luckily the silent one has bolts instead of rivets so I could easily open it up.
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The corrosion doesn't look too bad to me. The wires aren't broken. I used some sandpaper to try to clean between the contacts. The contact default state appears to be closed. Is that correct? It takes a surprising amount of pressure to separate the two.

What possible issues could there be with the diaphragm, other than it being perforated?

I found a couple threads where people started to discuss possible causes, but stopped short of recommended any repair procedures.

Thanks.

Found this on the Samba,

12V Hella Horn repair

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I have found the most commin problem is corroded contact points.

That's what I was looking for. Thanks Garland