@dc42 Thank you for taking the time to read my modifications.
MatterHackers has both Z-axis steppers wired to the same driver on the Azteeg. There is a much higher load on the left stepper due to the weight of the X-axis stepper motor and hardware mounts. The right stepper motor always eventually becomes out of sync from the left, further in advance. This is worse during long prints or when Z-lift is used during the print.
It is definitely a problem as I see software to auto level the gantry for both Duet and Marlin. I didn't want to run the software in between prints and I wanted to take the misalignment possibility out of the equation.
There was no leadscrew binding that I was aware of. And I had replaced the electrical connections between the two stepper motors twice. It is possible there was not enough current output since both Z-axis motors were sharing 1200ma from a single driver. Z acceleration was set to 500 in Marlin and now I only have it set to 20 in rrf.
For most plastics, if you are misaligned by 0.25 - 0.35mm at first layer, this is not as much of a problem. But when printing higher temperature plastics, such as nylon-ultem-peek, this becomes a real issue fast as these require a very critical first layer height.