This might seem daft, but is the mounting hole central? Manufacturing errors do happen, and quality inspectors do sometimes "let one through". I suggest this as I have a brushless motor that vibrates, I thought the shaft was bent and replaced it, there was no reduction in the vibration. Eventually and by accident, I found that the mounting hole for the prop shaft had not been drilled correctly and is at a slight angle, this throws the motor completely off balance. Unfortunately the motor was a Giant Shark purchase, just before they closed down so no chance of a replacement.