Interesting thread here.
Usually while I clean old calculators etc. I change electrolytic capacitor for modern film types. Usually They're not much bigger and they'll never need replacing ever again or at least for the next many many decades.
Sometimes they can't be as big as the original electrolytic ones but really even a smaller value filmtype will do the purpose of the original electrolyte better that it did in it's days. Changing them in the PSU/inverter on many VFD seems to have an instant impact. Display is visible brigther and more crisp even nothing else was changed. Changing tantalums usually makes no difference. Here I only do it if I by no means want them to fail.
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I have two counter-examples for this. I have two calculators: a Ti-68 and an Elorg-51. Both stored for years in a box without batteries, and with silica-gel to keep humidity low.
The Ti-68 developed a fault at the flex cable connecting the display to the motherboard. Even though it doesn't move or actually flex in the Ti68, still it got degraded somehow, leading to display problems (in my case, no decimal point was displayed).
That can usually be repaired. Also I believe it's from a manufacturing defect right from the start only that it didn't show right from start. Yes of course the materials changed a little or the tracks it was bonded to oxidized underneath or similar because of insufficient heat setting and that's why there's now loose connections. But as said that can be fixed in many cases and without any special tools. All you need is a soldering iron and some heat resistant silicone rubber or just a piece of bicycle tube although that'll melt slowly but it's useable (and it smells "great" too).
Find the spot to press to have missing segments visible. That's where to "solder". Put the piece of (silicone)rubber over the place and heat until it seems to have seated properly. The rubber gently distributes the heat, making dosing easy and therefore does not stick to the outer side unless you've heated it too much. Quite difficult to explain when it has got enough (not too much) to get a few dollar store calculators to practice on - really it's not that hard. Also to not heat at the very edge of the place as heat and the edge could cause track to melt over. But hey you can get conductive paint if you're so unlucky.
First tried this myself on a TI-30Xa instead of just throwing it out and it has worked great ever since :) And since then on a few other things with same fault.
Happy practicing!