Hi there aokman,
Good on you for having the guts to delve deeply and show others how it is. I bought a new EQ6 Pro a year ago and have the same horrid sounds as it slews my 10" newt around. I followed a number of articles to do a strip down of the bearings and re-greased and backlash adjustment, but to be honest, it didn't have as big an impact on the noises as I wanted. I did not, however venture into the motor gearboxes. It looks like you've identified the source. I shall save these pics and give it a go when I feel brave.
Thanks,
Bruce