Your vehicle gets a test drive (if driveable) and computerized diagnostic test to determine the nature of the fault. This could be due to a clutch problem, gear lever assembly, faulty sensor or wiring damage. These are fairly straightforward and quick to repair. If the fault is worn or damaged internal mechanical components, the transmission must be stripped down to identify these and furnish a repair quote, which takes a day or two. Parts availability from suppliers is the only factor that can affect the duration of a repair beyond a few days. RDG branches maintain a stock of Reman Exchange gearboxes for the most popular vehicle models which can be swapped out within two working days.