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!
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