This is a Great project!!!
solving the X Y Z coordinates into a delta system in a small amount of code takes real skills. I for one would like to see your code.
Mechanical problems that reduce repeatability are not unusual and take a great deal of effort (as in rebuilds) to resolve. A little preload to change the stress on your positioning members from compression to tensile might resolve some of your difficulties while keeping everything light weight.
This is a Great job showing a tremendous skill set.
If you decide to share your code my email is Johnk36333@hotmail.com