Extremely high quality OEM replacement gearbox seals and bearings kits from Synchrotech, these kits do not include differential bearings which can be purchased separately.
Renewing gearbox seals is a best practice when opening any transmission casing, gearbox seals perform the important task of making sure that your gearbox stays properly lubricated. With the average gearbox holding somewhere in the region of 2.5 litres of oil, it only takes a drop in the level to less than 2 litres to run the risk of serious trouble. The consequences can range anywhere between a less than satisfactory gear change to your gearbox eventually seizing.
When fitting and handling any oil seal, keep it and its sealing point absolutely free from dirt and grit. Make sure you fit the seal the right way round. The lip (or lips) always faces the oil it is sealing.
For most rebuilds bearings are also replaced. Bearings commonly fail after tens of thousands of miles, worn or defective bearings will screech or vibrate eventually causing damage between components which were originally designed to have little to no friction between them.
It's common during the rebuild process to have on-hand replacement sets of parts, as the removal of gearboxes means for many they're currently without a car.