How would you repair faulty synchroniser unit gearbox?

To repair a faulty synchroniser unit in a gearbox, first, remove the gearbox from the vehicle and disassemble it to access the synchroniser. Inspect the synchroniser components, including the rings and sleeves, for wear or damage, and replace any faulty parts. Clean the components thoroughly and reassemble the gearbox, ensuring proper alignment and lubrication. Finally, reinstall the gearbox in the vehicle, test it to ensure proper operation, and check for any leaks.