After I saw that user „James VanDusen“ posted about „8mm m8 threaded rod“ in the MPCNC forum https://www.vicious1.com/forum/ I decided to do all these steps to try it out. So this morning I dissassembled everything around the rod, printed out the new part F-XYZ_T8.stl from https://www.vicious1.com. In my case (25 mm IE version) you can find it here: https://www.thingiverse.com/thing:790533/#files
So after thinking about it and because I hadn’t another M8 nut here but a 8mm linear ball bearing I will give this a try: A new designed F-Nutlock.
First impression of the new assembled z-axis with T8 leadscrew upgrade: