If you have an old calculator and you find the buttons are sticking, you can sometimes fix it with a bath in isopropanol. I have revived 2 old HPs this way.

1. take out batteries

2. fill a shallow container with IPA (70% or 90% is ok)

3. immerse buttons, but try and keep the display out of the IPA as much as possible (if liquid gets in the display it takes forever to dry and can leave a ring)

4. work the buttons until you feel improvement, IPA will turn brown

5. let dry for a few days before you put batteries back in.