Starter jammed in flywheel.

[signsup]

Had similar problem on Model T. Recommended quick fix was to rock the T, but we never could get that to work, loosen screws holding starter in position and the bendix would spring back, tighten screws and be on our way.
Our problem was bent ring gear and when it jammed, rocking the car would not change the angle of the bendix teeth into the ring gear, so it never solved the problem until we removed ring gear, straightened out and replace.
It was suggested that running starter on 12v for a system designed for 6v was overpowering the thin ring gear metal.
Hope your problem is solved, but the rocking motion not providing a fix sounds like it may be the angle of attack, not worn teeth on either ring gear or bendix.
JMO