And I'm back to this.
Mostly back together:
I plugged it in, flicked the switch and was rewarded by a humming noise and no motion. It would run if giving a helping spin to start it, which suggests a winding or capacitor problem. There's no capacitor so it's the windings. This motor has a centrifugal switch for the start windings. So off and apart came the motor and I found this:
It should, and now does, look like this:
All back together and it runs smoothly.
What looks like metal filings is just paint overspray.