the nuts should fix that and keeping the springs really tight and having the two parts of the frame bolted to something solid :-)
Mind you the ebay bods were doing a cheap probe with the board and screen and driver kits for acouple of quid.
But too much fuss.

What does your z axis endstop setup look like ?

Modified mine to simply screw up and down and hold in whatever place you set it. Before it had three tiny nuts you had to piss about with.