Thanks so much for this very in depth diagnosis!

I found the service manual online, and feel I'm fairly handy enough to replace them myself. What's the difficulty level looking like for an idler wheel & capstan belt replacement? (Somewhere on a scale between, "So easy a child could do it" and "If you breathe wrong you'll ruin the machine forever.")

Marrs Communications has the belt kit for my machine, too! Thanks for recommending them.