How is the bowl sealed to the flange? In the USA, the majority of toilets use a wax ring to provide the seal. If the toilet can rock in the least, it will break that seal since the wax won't rebound once it is compressed. Shims may be necessary. THen, in most places in the USA, require the toilet/floor joint to be caulked. This does a couple of things: it helps keep the toilet in place, and, it prevents near misses, dirty mop water, etc., to seep underneath the rim. Just not sure how things are typically done down under there...(hope to visit one day!).