Only on long journeys, the clutch will push down and come back up 5cm. I put my toe under it it release all the way up. This has happened three times on 200km journeys . I had the clutch master cylinder replaced and the problem reoccured next long trip. Trips less than50 km are usual for me and the problem doesn't happen. so its hard to demonstrate to the mechanic. Any clues ? HELLLP