By adjusting the stepper motor position I assume you mean just loosening the screws a bit and wiggling it around to reposition it slightly? Tried that too.
No grease on the sensor. I checked it under microscrope (while still installed). I tried brushing it and blasting with compressed air to clean any dust, no difference. I also tried adjusting it's position ever so slightly, but still have the same behavior.
Working on salvaging a Macintosh 128K. System powers on fine and displays the floppy logo, waiting for a disk to bootup. However, the Sony MP-F51W-03 floppy drive did not work. Disassembled it, cleaned and relubed everything and replaced the eject gear. Now the eject mechanism works nicely...