Well, I assembled the 12-50 zoom gear, and the instructions are clear enough. My issue was more user issues- the screws are very small, and between my bifocals and large fingers it was somewhat challenging to assemble. Fortunately I had the foresight to assemble it over a tray which repeatedly caught the dropped screws.
Question- after assembling everything and installing it in the housing, do you have to turn the zoom knob on the housing with a fair amount of pressure to change the zoom length (as compared to other zoom gears). Also, it zooms slowly. Not so much a problem, because it will give a fair amount of control with video, but more a check to make sure I shouldn't need to pull out my aforementioned tray and disassemble/reassemble to zoom ring. The Macro/zoom switch on the port works fine.
I found it take some pressure to change the zoom length and it zooms slowly!
The quickest way is to use the Fish mode, so from 12 to 50mm, or 50 to 12mm is just a click!