When the gearbox malfunctions the problem often requires to remove the gearbox from the engine itself. This is done by lifting the car and bolting off the gearbox. The operation is a fairly advanced procedure and requires help from several mechanics to be done propertly.
The problem can be solved either by changing parts like the lamels or for example the flywheel when they have been exposed to wear due to for example frequent slipping with the coupling. Another problem might be wear on the gears like below.