I've got a 66 plate 2 Litre diesel Kuga with hydraulic clutch system, thepedal has started not returning at times when gear bchanging. there seems to be a point where the pedal sticks slightly, and sometimes it jams fully down to the floor. The fluid level is correct, and when pumping the pedal it never sticks. Has anyone had this problem? If so, what's the way to stop it?