Paul:
I was digging through some boxes of stuff I have and found this:
http://www.beisensors.com/pdfs/L25-o...al-encoder.pdf
It's a sooooper high precision (2540 cycles/turn) encoder.
It's got a 1/4" shaft with a flat on it, so it doesn't really meet your motor's requirements, but if we could figure out a way to connect it, it may work.
Does the motor have a shaft out the back?
- E*clipse