renault traffic?

We got a Renault Traffic van, its done 37,000 miles and the Gear Box went on it.
It has now had a new Gear Box fitted and still a problem! First thing bin the morning after its been standing all night, this is what happens: We start the engine put in to reverse, to reverse of the drive and its fine. Then foot on clutch ready for putting it in first, but the gear stick wont go in to gear at all, until you take your foot off the clutch and find the clutch has gone flat, so you put your foot under the clutch and pull it up, then once pulled up it goes into gear. Have taken back to the garage 4 times, they keep bleeding it and still like it! Then today, he said it could be the Master Cylinder, thieve now checked it and said no leak from so don’t know what to do, we were suppose to be selling it tomorrow to a friend , what a night mare can you help ?