Not working Twiggy Drive – help wanted

Hi,
I’ve got one Twiggy drive working and one NOT working in Apple Lisa 1.
Not working means: After inserting the disc you can hear a terrible rattling sound from step motor. Head is not moving as usual. Disc rotator is working. Only heads will not move anywhere.
I tried to push the spindle of the step motor with a screwdriver but it will not move. The rattling is not stopping and you can’t use Lisa (cursor is hour glass). Even the power switch is not working.
I tried cleaning and made some basic checks for the electronic parts. Everything looks good.
Any ideas? If the step motor is gone, any ideas to find spare part?
Thanks!