HP-50G trying to fix failed keys

[HPing]

I recently purchased an HP-50G from eBay and some keys don't work. Kindly looking for tips from gurus to (try to) fix the keys.

Back story- The eBay seller kindly reversed all the charges. I would like to fix the HP and pay him back, if possible. It would be a fun project with no financial downside.

Errors - Three keys don't work (0 . G).

- There seemed to be the slightest bit of crud around these keys which I could see in daylight. At one point maybe there was more crud but some was cleaned and some fell inside the calculator.

- I tried a bunch of things to the calculator to get the keys to work (remove batteries, self-test, set beeper with keystrokes, press the keys multiple times...).

This post gets me pretty far in the disassembly. But once the case is split, I'm not so clear on further disassembly and typical key fixes. Could someone provide some tips? Thank you.
https://www.hpmuseum.org/cgi-sys/cgiwrap...ead=171784