Clearance on modern clutches is minimal, typical dealer, wrong diagnosis. If the car selects gear with the engine off, it must be the bit between the engine and the gearbox. It may just be air in the clutch system as the Clutch will have plenty of meat on it. Or the springs on the clutch plate have gone soft, due to excessive heat, town driving or racing starts. I bled my clutch after being told my clutch needed replacing at a cost of £1600, but Renault we're going to pay half. Anyway, an hour or so under the car and a total fluid change, 10000 miles later, my gearshift is a lot better than it left the stealer.
Apparently Renault throw boxes in left right and centre, when it is not the box, it can be linkage setup, but more likely to be Clutch related after a number of miles due to clearance between the clutch release and the plate. The oil causes problems due to the materials used on the baulk rings which causes them to stick together, it maybe that good old ATF fluid may sort this out, looking for a culprit, volunteer, with a bad/crunchy box to try this.