It’s not like the old days when Mini Coopers did appeal the purists and a manual was the only thing to have, today’s Mini buyers a less purists than fashion followers. Although I would prefer a manual for the fun of driving it, most buyers would prefer an auto and that would affect the resale of your car should you choose a manual. I do agree with you that it’s a good idea for your son to learn to drive a manual.

To register the vehicle in Victoria you will need to get a roadworthy certificate, pay a transfer fee of $38.50, and pay duty. The duty is based on the market value of the car, and is calculated at $8.40 per $200 of that market value.

You've always got the right to argue your case and try to negotiate a satisfactory outcome, but I doubt you would be successful with a car as old as yours. Unless you're prepared to invest a lot of time in the negotiations I would suggest you just cop it and get on with life.