ANNIN ROBOTICS

Looks interesting but I am not sure if it will handle the force. There are some fibre enforced filiaments which might do the trick.

The "Keyed Rotary shaft 8mm" is difficult to get in europe. I have been looking for it quite a while and the only source I found was: https://www.raptorsupplies.com/pd/keyshaft/8mm-gks-1045-300?web_source=DE&web_medium=header+country+flag (free shipping, at least to Germany...) In the end I used a normal rotary shaft and modified it a bit, so that the setscrews do the rest. Not the best solution, I guess but I could not convice myself to pay the price...

I had the same problem with j4/j5/j6 which are all on the same rj45 connector and in the end it was a faulty rj45 cable