Well I'm sorry to tell you Mildman but you can't fill the gearbox through the gear lever hole! And I can't see how you could fill it through the breather when it's still in the car either- the breather pipe is at the top of the gearbox, and it is a sort of a hook shape, and it is only about 1/4" dia. and the air would have to come out of that breather as the oil displaced it so it'd be a pretty neat trick if you could fill it through the filler in place!

Damn that plug must be tight. I'll assume that when you heated the housing you aimed it square to the gearbox and heated the ali housing around the plug, and didn't aim the flame at the plug like your pic shows....