Mechanical on UA to SYD

Not sure if there is a thread about this already (if so, I couldnt find it).

United made the Sydney 6pm News tonight with the announcement that their 747 (UA6872 - strange flight number) had to do an emergency landing in Sydney around 5pm tonight. They dumped fuel over the ocean first. Apparently there was only crew on board.

Anyone know if this was a re-positioning flight or what it might have been for?

Thanks :)