Dear all,
after removing the bars from step 573 and the bar of step 89 I was able to reach the 8 pins of step 63. After removing these pins I was able to lift the complete top of the crane for entering the gearbox to notice that I used the wrong pins (too long) in step 73.
Note: For reaching the pins of step 63 I also had to make some room by lifting (slightly forcing) the bars of step 84 from the rings below.
As there were no shorter pins available, I just used pliers to cut them into the correct length.
Put everything back together, and all works fine now!
So, for others knowledge, there is a ‘shortcut’ to reach the gears 😁