How to repair the horn switch on a de luxe model

So some of the de luxe models of Mopars in the '70s and '80s had a large horn switch with a wood-grain inlay in the switch's vinyl cover. The switch consisted of a concave sheet metal base that attaches to the steering wheel; the base is covered by thin perforated foam in the center, and over the foam goes a concave brass plate that has little teeth that contact the sheet metal base through the perforations in the foam when you push on the vinyl covering.

I can post a picture if necessary.

When the foam dries out and fails to insulate the brass plate from the metal base, the horn stays on all the time.

Would anybody have any suggestions about how to repair a horn switch like this?

Thanks a lot.