Just another disc cap for a switch. Like the 470 Pico farad.

http://www.taydaelectronics.com/capacitors/ceramic-disc-capacitors/10-x-0-047uf-50v-ceramic-disc-capacitor-pkg-of-10.html

Stock up, they are cheap.

But, this would not stop it from registering. Just stop it from registering quick hits. If you trigger it by hand and it does not register this is not your issue. The cap simply adds a delay so a slow old CPU can register while scanning. And if it was shorted it would register all the time.

Also, did you do anything to it? We had a guy once who ran the plumb-bob assembly parts through a tumbler / polisher and wanted to keep it clean and shiny so he hit it with a few shots of clear.