Clutch pedal sticking

Had a issue with my octavia vrs mk3 for a week now. 

Basically the clutch pedal was sticking half way on realeasing pedal. Mechanic checked no leaks was told its master cylinder they go faulty, so i changed the master cylinder and got the brake fluid changed and pressure bled. All seemed fine then 2 days ago pedal stuck to the floor pumped it went better until today after 170 miles the problem started happening yet again.

I inspected the brake fluid reservoir level same at max could see dirt build up at top of tank basically it looks contaminated also weirdly i inspected the clutch pedal area and i could see my pedal wet its defo oil its slippery. I just had the master cylinder changed on friday how is this possible prior to changing the master cylinder there was no leak this just happend since i got it changed instead of making my problem better it has gotten worse. Any help would be much appreciated.