Answer to: How can I fix calibration problem?I had the same issue here Steve, hopefully you can replace your optical encoder and solve the problem. If your encoder isn't too damaged you can try adding a dab of glue on the center. It may hold just enough to fix it permanently. I fixed mine that way as a temporary solution until I can get a new encoder in there. Maybe you can repair it too if it isn't as badly cracked as mine was.
Answer to: How can I fix calibration problem?Hi Steve, This is a common problem you describe. It has been verified that a number of G27 controllers have a cracked optical encoder wheel (the part that senses wheel position & calibration). The cracked optical wheel tends to slip during usage and hence you end up with a miscalibrated G27. I'm currently working with CM Laser Service to test a laser-cut solid brass encoder wheel that will replace the flimsy plastic one that came with my G27. The replacement part is expected to out-live the G27's other components since its a metallic part that cannot crack under normal usage conditions. Once we complete the test I am willing to make an iFixit guide detailing the whole replacement procedure. The new part will be available for sale from CM Laser Service Stay Tuned!