I just found a SHARP EL-5020 scientific "programmable" (though how, I've no idea) at the Goodwill for $0.99 . Upon cursory check-out, most everything worked but the "8" and "9" keys. (?!?!) (Curiously, but even though they didn't register, the LCD display dimmed slightly as I pressed them.) Also, the memories weren't "continuous", like I expected them to be.
I took the case apart, and found the keyboard assembly is held together by heat stakes. While accepting that I probably had to take that apart, I noticed the pad for the tiny "Reset" button that's hidden on the back case. I put it together, pressed "Reset", and voila! Full functionality restored!
Repair Lesson 1a: Try the Reset button, first.
Also, the vinyl hinge holding the calculator to its little vinyl "wallet" is cracking -- I suppose I might try vinyl cement (as is provided with swimming pool repair kits), but I'll accept other recommendations, should some of you have any . . .