HP 21 not powering on - repair/troubleshooting advice

[dmh]

Unfortunately the '4' key has stopped working again.

I've tried the same steps again as previously recommended but no go (including a drop of alcohol).

All other keys are still fine ('5' double bounces sometimes) so is this still just the key switch or could it be something else?

I don't think I'm up to pulling the keyboard apart.

The unit is so clean and nice in every other way :-(