The fluid in the clutch hydraulic system should be changed ocasionally, just like the brake fluid. You will need to go through a bleeding process to change the fluid.
Also, you may have a little air in the system after time and need to bleed the system to get the air out. The usual symptom is that the clutch will not fully disengage or that the clutch pedal feels a little spongy.
I change my brake fluid once a year. I sometimes skip the clutch part of it so that it might go two years.
If you don't change the fluid it will eventually take on moisture which will corrode internal parts and eventually cause them to fail. Fluid changes will help these parts last much longer. In the case of brake fluid, oil fluid with some moisture will boil at a lower temperature, creating a higher likelyhood of brake fade with extreme braking.
