My two pennies worth...
I repair Industrial ABB circuit boards for my day job,,,,,
Rule 1, See a little square Tant cap in a circuit that don't work he be the prime suspect (usually dead short)
Why do ABB love those 6.8uf / 35v things....Pain is the arse to source?
BR
Andy
Because that was a standard value, high enough to be useful, but not a 10uF unit which cost twice the price.
I changed many over the years, especially in avionics, mostly the solid slug type which had failed due to them being the cheap ones ( for solid slug that is) with a rubber seal that degraded with time. I used regular aluminium electrolytics as replacements in most cases, just because I could not source the proper ones ( a little sanctions thing), and had a 2 pallet list of everything with the word "cap" in it from stores as a guide to get the stuff out from existing stock. I found a lot of 1000 10uF 10V units in there that had been sitting since the 1970's, and tested 200 before giving up, the only failure was me putting it in backwards and applying 10V with a current limit of 10A. then I used them as small howitzers, especially the ones I removed which still had some capacitance and thus some electolyte. They do go through thin board at short range though you needed the 28VDC bus rail with the 50A breaker to get the full effect.
The dry ones will go crispy, especially the orange or blue ones, the older coloured band units were a lot more reliable, probably because those have not been made for 40 years so all the early failures would have gone bang by now. The orange would burn through the board, the blue ones would just burn.
I wonder how those ceramic caps will behave with time, I am very suspicious of them, as they are both thin, exposed to contaminants ( no real seal on the active layer) and they have had reliability issues. Ask anybody who used those first gen ceramic decoupling caps in glass tubes, or the yellow dipped cases, and how many caught fire on 5V rails in computers. I have seen them lit up like a lamp on the board, as the power supply was not quite capable of blowing them out, and had the overcurrent limit drop the voltage to around 3V with no foldback.