If you’re not set on having an OEM Toyota horn button you might be able to snag a 3d printed one from a member on MUD.
https://forum.ih8mud.com/threads/1970-fj40-horn-button-image.1271785/
I used the blaster stuff last fall on my sequoia to try and keep some of the salt at bay over the winter here up in Alaska. It comes out of the can thick. I looked at it recently and it was still soaked on there really well. Seems to do the job.