Web Master:
This could be either a nitrogen and sulphur deficiency, a lack of water, or both.
The remedy for this is simple - give the soil a good soaking and then apply some Sulphate of Ammonia (which is rich in both Sulphur and Nitrogen).
It could also be an issue with cold, though Baulkham Hills should be OK. They are slated to grow well down to climate zone 9 which covers most of lower altitude NSW, though cold nights will decrease its ability to draw up moisture and associated nutrients.
If it starts to drop leaves from the lower part of the plant then its definitely lack of water. Apply a wetting agent as you soil may have become hydrophobic due to the waxes in the fallen foliage coating soil particles.