Replacing your vehicle's gearbox oil is usually a surprisingly straightforward task that is commonly overlooked. There's generally nothing too much to be daunted by... in fact replacing gear oil is normally a very similar process to changing engine oil.
Running a high quality gear fluid not only ensures smooth gear change but is vital for the protection of internal components and gear faces / teeth. Even if your vehicle manufacture states that the gearbox is 'fill for life', you'll quite often find it still has a drain and replacement time scale... so well worth checking.
3 sizes available