I gave up on replacing or repairing the back gear.
Instead I got a 20WATT Motor speed controller, with it and by moving the drive motor to its lower drive pulley (it came with two speeds) I am able to drop my spindle speed to near as slow as it spun with the back gear and then dial in down just a little bit with the electronic speed controller.
Spinning just the chuck looks good, how well it will run under a working load I do not know but hope it will get it done.
There are few jobs that I needed the back gear for, as 90% of my work it at its highest speeds.
Rich