Which gear does it crunch in? 1,2,3,4,5 or reverse?
If it only crunches in ONE gear, the most likely cause will be the synchohub /baulk rings on that gear. If its all gears, then its probably a clutch related fault. Is the clutch "biting" point on the floor or near the top of the clutch travel?
If its only one gear, then the box will have to be removed, stripped and faulty parts replaced. Not a home job as there are too many spacial tools required to repair it.
Hope that helps
Bob RTE