Capstan or idler wheel? I call the phenolic part attached to the motor spindle the "capstan."
http://www.terrysrubberrollers.com/ does the wheels.
I think I have an extra 33 wheel but if you're serious about it, it might be worth getting a fresh rebuild.
If the phenolic stepped spindle thing is out of round, that could be tricky.
Does your T12 have an Eastern Air motor or an Ashland? That would make it a T-12H (hysteresis synchronous motor).
If you want to try a different 33 wheel look me up in two weeks. I'm off to the MunichHighEnd show tomorrow. Pork and beer non-stop! Roscoe would love it there. I love it there.
Also, before you even replace the wheel, check the 2uF phasing cap. Mine was leaky as hell, got hot to the touch within minutes, and caused the motor to shake like crazy.