I'd keep cleaning until it works. :7 Especially as it did work briefly for you.

What's the model number of the keyboard. Maybe if nothing else works, a Google search might turn up an identical board.

There are keyboard re-mapper programs but I don't know what you would re-map to be a "z". Maybe the tilde but it probably would take awhile to re-map your mind.

Will capital "z" display?

Jim.