by Droopsnoot backup » Fri Oct 28, 2005 10:05 pm
Halfords used to sell a suitable tool, like a bar with multiple large protrusions on it. Like those four-way wheelbraces you see that have a different size socket on each corner. The idea was that the same tool covered most filler plugs. Some were square as I recall.
I think you're right about the level - make sure the car is level, then fill the box until it starts to run out of the filler hole. Often helps if you put the bottles of gearbox oil in warm water to make it easier to pour.