Also check to see if the idler and the pivot joint that it's mounted to move freely. It should move outward to apply pressure against the inside rim of the platter to keep it spinning. There is a long spring underneath, and I can't remember if it keeps the idler away from the motor shaft and rim when not turned on (to prevent flat spots on the wheel), or to help keep pressure against the inner rim when in operation.
I've been in this new house for almost two years and haven't gotten around to tending to some of my ailing Maggies. If you're careful and stick to one section, and not poking and prodding in other areas, you should be able to figure out the spinning issue.
Folks around here rolled their eyes at me when I asked if they could repair my babies. You'd have thought I was speaking in tongues without an interpreter...LOL! So I took it upon my self to join a few phono boards about 15 years ago and soaked up as much info as I could from hobbyists, retired techs, etc., even bought some new/used books on electronics and circuits.
Finally armed with some knowledge from those older newsgroups, soldering guns, meters, etc., I got busy. I am mechanically inclined and like to know what makes things tick. Yes, there were some mishaps along the way, but....as another repair came along, I learned from the mistakes of a previous repair, and it was slowly getting easier.
The mechanical part was a piece of cake, but then came the electronics...that's a whole new ball field and really got your brain going. Tracing a signal through the audio chain to find ailing components, testing/replacing electrolytics and other semiconductors (alot of them are labeled so you don't always need a schematic), it goes on and on.
I am no professional by any means, but I've managed to repair everything that came across my threshold, including 8-tracks, reel-to-reels, cassette decks (mostly belt issues), with occasional help from internet friends over the years. I'm just alittle leary about TV's with their high voltages
It seems almost impossible to find folks locally to work on our units, and if you do find someone way across the country, then you need to know how to remove that turntable or receiver/amp, pack it up, pay for shipping/insurance, pay for labor and parts, pay for return shipping and re-install everything yourself.
I can't imagine what someone would have charged me to go through all that shipping drama just to replace a dozen or so electrolytics and everything else was okay. And, everyone out there isn't honest and your eyes may pop when you see the final bill. If you are all thumbs and have absolutely no knowledge about these units, then you have no choice but to send it off to someone.
I'm not on a soap box here, just trying to justify my "hobby" as an amateur and have had many successes, and why I choose NOT to send my stuff off to a professional. They do have alot to offer and have offered it freely over the web, and that's where I acquired most of my knowledge.
Hey, Thom...you build pipe organs, what an art and a craft. I admire you for that and it's something that you don't learn overnight. I've played a few of them back in the day, but I stick to those screaming Hammonds and Leslies for now. Gotta get my Gospel, Jazz and Blues on!

For the more tender side, I do keep a 9-ft Concert Grand in the living room for some Bach, Schubert, Mozart and Beethoven. --BB
Sorry for the rambling...insomnia.