Gearbox oil change

[Perfection]

Just given a new life to the gearbox by changing the oil. Bought oil and asked my independent garage to drain and put in the new oil.

The manual states it requires 2.3 litres of oil for our 2.0 diesel model. When it was drained we managed to drained 2.2 litres. 

Then we managed to put in approx. 2.5 litres. Seems quite a significant discrepancy. 

Anyone got any comment or explanation with regards to the difference?

However, there is no issue with the gearbox engagement. It is much smoother than before the oil change.

 

[Perfection]

Replacing gearbox oil second times. I am going to replace drain washer this time. Does anyone know what the plug seals/washer size is? Is it the same as the sump plug washer?