Can I put an electrolytic motor start capacitor on DC permanently?
The manufacturer states these capacitors are designed only for intermittent use with a low duty cycle:


  KEMET's MS/MD Series of aluminum electrolytic capacitors are designed
  for i[n]termittent duty only


and


  The standard rating is 1.67% or 1/60th full time and corresponds to a
  maximum duty of 20 starts, each of three seconds duration per hour. It
  is expressed as 3/1.67 (a 3 minute cycle with 1.67% duration during
  which the capacitor may be energized). If the same capacitor is to be
  used for a duty cycle of 60 starts per hour the cycle duration will be
  1 minute. The operation time per cycle will then have to be reduced to
  1.67% of 1 minute (i.e. 1 second). Alternative duty cycles are available on request.


As such, using them with a constant DC voltage is out of spec, and you're on your own - there's no guarantee they'll function, or for how long.