aside from the amazingness of that link you shared, your post prompted me to open up the 414 more so than I’d already done because I didn’t realize the capstan itself was a moving part with the pinch roller!!
so tonight I opened it up again, and this time unmounted the actual… uh … tape deck and motor part (sorry I don’t know a lot of the correct part names and such yet), and I noticed the capstan is connected to this big wheel underneath, and with a belt directly connected to the motor.
Then as I was handing the deck assembly, i accidentally pressed in on the capstan wheel and it moved! Upon further investigation, I deduced that what’s happening is that the capstan is sliding down when the deck is mounted, and the teeny tiny gear (barely visible in the shadows of the pic below) on the capstan isn’t connecting with gears connecting to the right reel.
Note I pulled this out further than it actually was for the sake of the picture. But certainly it’s not supposed to be like this?
I ordered a service manual on ebay*, but any suggestions on this until it arrives?
*I literally could not find it anywhere else so when I get it I will happily scan it and share it with anyone who needs it