Cause

In case of CSC, Concentrated Slave Cylinder, internal piston not traveling smoothly causes system failure,
and it may result in following symptom;

Difficult to disengage gear:

1) Fixing or sticky movement causes short stroke and results in difficult to disengage.
2) Leaking of causes short stroke and results in difficult to disengage.

Slipping clutch:

1) Oil on a friction facing due to leakage from cylinder assembly causes slipping clutch.
2) In case of malfunction in regard to piston return, it causes continuous semi-disengagement and results in slipping clutch as well as facing abnormal wear and burnt by burnout.

Solution

Always replace with new cylinder assembly. Install cylinder assembly after ensuring smooth movement.