I took my X axis off last week and opened up the Ball nut on both my Y axis.
I noticed my left Y rail was harder to move by hand than my right rail (with cnc turned off).
I gave the ball joints on both rails a cleaning and a proper lube job.
Now I have the machine running fine at Max Velocity at 10 instead of 5!
The video below shows the process.
I also installed a proper dust collection system.
Goes to show that proper lubrication and cleaning can solve many issues!