Over the years I’ve tried various oil pumps but not had long lived success with any of them.
For filling gearboxes and axles I buy a 5 litre bottle of oil (far better value than buying by the litre) and just keep refilling an old 1 litre plastic gear oil bottle. This is the round section type with a pull out spout/tube. The problem of not being able to get all the contents out is solved by pushing a length of flexible plastic tubing over the pull out tube so that the bottle can be fully inverted and held above the filler aperture.
Warming the oil in a bucket of hot water helps it flow quicker.