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The starting capacitor for the middle basement Duo Therm a/c unit has finally given up. 35 years is a good run. It does look original and unmolested. I thought it prudent to replace the start and run capacitors at the same time, although the run capacitor meters out just fine. Both replacement capacitors are smaller than original, although the run capacitor is 1/3  the size of original, but has the same spec 370 volt 5 uf or mf. Is it because the originals were made in America and the are Chinesium? Am I missing something? I have not installed these yet because of these questions.
Guy,

If you are replacing with the same MFD rating and the same voltage rating you will be OK.

Obviously disconnect the power, and confirm it is disconnected with a voltmeter. Then take a screwdriver and short the terminals on the capacitors before digging in there. It could save you a nasty shock, those caps pack a wallop.
Thank you Richard. That is a lesson I learned a few years ago. It really gave me a zap.  I was able to see the spark going to my finger.