You can buy a new, complete diff for next to nothing from people who part these cars out and sell them on eBay. Here is one, for example, for $16 plus shipping. http://cgi.ebay.com/NEW-OFNA-HYPER-7...3286.m20.l1116

That's the great thing about Hypers....parts are so readily available. Fill it with 3000 wt. fluid and you are good to go.

Because it is small, postage to Australia shouldn't be too bad.

Hope this helps.