I have a 2005 Toyota Corolla Verso 2.0 D4D (UK model). The clutch does not disengage fully with clutch pedal fully pressed. This is a hydraulic clutch. When in gear and brake is released with clutch pedal fully pressed it will creep forward very slowly. The main issue is difficulty changing gears when stationary or downshifting. There is no loss of fluid (this car uses the brake fluid reservoir) or visible leakage. The clutch pedal feels firm all the way to the floor. Is there or any further diagnosis I can do? Or do I have to disassemble the master and slave cylinder next?
Check for a master cylinder leak by checking the firewall behind/underneath the clutch pedal for fluid. You can start having disengagement issues with leaks small enough that the fluid loss won't be noticeable. Repairing them is typically not done anymore, take it in and swap for a fresh factory unit. Not sure where the slave cylinder is on that model, but you should check that too if you can. While I've seen a number of master cylinder failures, I've yet to ever see a slave cylinder failure on the cars I've looked at. A very rare possibility is that just bleeding the fluid will help (I have seen a car where someone overheated the clutch to the point that the fluid in the nearby hydraulics boiled!).