If any of you out there are having problems getting the brass filler plug out of the diff, buy yourself an electric wheel wrench. These cost about £15 but are worth their weight in gold if you don't have access to air tools. Intended for tight wheel nuts, they just plug into the cigar lighter socket. I spent ages under the car with a 13mm allen key and a hammer (for shock tactics), to no avail, so I used a short section of the allen key and the electric wrench. Brilliant!
Also good on Alfa alloys!
