I have a 2011 FE450, not a FE570, but I just discovered the hard way, that there is a generic design problem with the OEM clutch slave cylinder, definitely with the 2009 through 2011, and any KTM models that use the same slave clutch P/N 75032061044. It is a basic design problem, the clutch piston has only one O-ring, the piston wobbles, and the O-ring leaks. Check the hydraulic reservoir level every ten hours and top up as necessary. Otherwise you end up with no clutch control.
I have ordered the Sigutech clutch slave cylinder from KTM Twins to hopefully solve this issue.
Cheers,
Blaine