Just to update people and perhaps offer a little encouragement to people who are in the queue themselves (or have parents in the queue) it looks as if our 804 visa is about to be finalized. We have got over the last hurdle which was the medical exam - despite having the usual medical problems of people in their seventies. There is still a problem with a mix-up between Centrelink and Commonwealth Bank over our assurance of support but sorting this out should be a formality. We first applied for the visa in September 2006 so the total waiting time has been a little more than seven years.
The final process started with a request for information on September 10 with a deadline of four weeks later. Because I was in England at the time the deadline was extended to October 30. In fact, I managed to beat the deadline and submitted the final information on October 22 so the final stage has taken almost exactly six weeks. The people from the Parent Centre in Perth were extremely efficient and cooperative throughout the process
Many thanks to all who have provided moral support through this thread and particularly to Gill (Gollywobbler) who started the thread. If I can help anyone else who is going through the process please don't hesitate to ask. I don't claim to be an expert but I can at least tell you what has happened to me.