ap for a very short time, so they must be robust enough to absorb that shoc k, repeatedly and reliably, in addition to the actual voltage involved. So, whereas the actual operating voltage may be say.... 240 VAC, the start-cap must be rated (at a minimum) of 150% of the operating voltage.
voltages are small, and the frequencies high.
apacitance than a start-cap (and whereas replacement voltage may be higher, replacement capacitance should remain very close or identical to OEM).
Of course motor rated caps have advantages. So do higher rated non-motor ca ps. But the key point the op appears to have not noticed is that his crude pape r cap has already lasted over 70 years. That is more than good enough.
NT