I would certainly take the cover off the motor & poke around a bit, checking all the solder connections. Also cleaning the constant voltage plug itself with QD electronics cleaner or alcohol, and brightening them up with fine sandpaper or a scotchbrite pad helps. Lastly, if you look closely you'll notice the switch's constant voltage plug is actually 4 separate pieces that form the circular male plug. You can ever so gently insert a razor or knife blade into the male plug, and slightly open it up to create a tighter fit inside the plug-in that's delivering the constant voltage.
Tom