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: (free shipping,...

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