Sticking clutch pedal 2012 focus

[Rockettvr]

As in the title- clutch pedal intermittently not returning all the way up after changing gear. Doesn’t do it all the time and will lift up easily with a toe underneath it. No clutch slip. Tried changing the little spring/yellow plastic assembly on the pedal but no change. Googled answers go from faulty delay valve to full replacement of entire assembly (master slave hydraulic lines the lot)
Anyone have a definitive answer to this before I start replacing random parts???
Many thanks

[vw_99]

If its a mk2 there was a moddified return spring set up.