Yeah I had a lot of trouble trying to map anything between SEA and SYD via the OZ site, its pretty terrible, doesn't know all its routes even though they exist (orbitz etc have them). Also its cheaper to use a travel agent (or orbitz etc) since even if you call their rate isn't the best. I wanted a bit of a strange itinary with directs from SEA instead of going through LAX like orbitz kept trying to force, so i ended up just sending a very custom request to a travel agent after looking up all the flights i wanted individually and having them craft it into one booking for me haha.