I was going nuts trying to eliminate that last bit of flex in my gantry.
From what I can tell part of it is the X axis rails twisting. The stiffening mod reduced it but did not eliminate it. It looks like it is the aluminum rail itself that is twisting. I don’t know if that last bit of twist can be eliminated without changing materials.
Part of it is coming form the Z axis assembly.
I gave up decided to do a Gantry Upgrade to C-Beam
But many people have reported good results replacing their Z axis. Either with a lineal rod setup from e-bay or a c-beam setup for open builds.
When disassembling mine the lower adjustable v wheel was really messed up on my z axis. The bracket hole damaged, the screw bent.
And there are roomers of a single gantry rail upgrade from inventables may be in the works.