Stolen from http://corvettec3.ca/tips.htm :
Here is my tip for fixing the horn retainer by eliminating the horn contact post and replacing it with a spring and wire. Yes, it is only a $20.00 item but any place you can save and fix it your self is a good thing. The horn cap retainer is a weak design, held together with plastic rivets. The key to this repair is the plastic bushings that can be found at any Ace Hardware store. I made a new insulator gasket out of plain gasket material as the old insulator usually is broken or missing. I guess the temperature spikes has a lot to do with it coming apart. I have used screws and nuts with locktite to hold it all together but have found pop rivets to be a lot cleaner. I have also eliminated the post and spring with a wire and spring. The pictures below will hopefully help with your repair.