re: #19 William Lewis

Is there a nib sticking up that allows you to press the key and have it be recognised? If so, you should be able to find a blank keycap and replace it. If not, then the external keyboard will be your best solution. Is it old enough to be PS/2 or can you use USB?

Yes — there is a nib that allows the “key” to be recognized BUT the keycap doesn’t stay attached. I am able to type by manually pressing the nib.