Just bought one and installed it yesterday. Lots of threads on this subject. Most complain like me that it's a bad design and keeps blowing O-rings. Took me awhile to figure out exactly which one to go with. First off, is your old one mounted on the top, bottom or sideways on the tractor...
I've been researching this same issue and on another thread he used crii.net kp05106csss pump. Don't know if you can just replace the shaft. Here is the thread. GC2310 Wrong Pump installed He shows pictures of the difference in the shaft. Curious as to what you finally ended up doing?