So I contacted the supplier and it evolved that currently Res-Med in Australia have a return policy within 30 days provided this is the first in the last 12 months. So back it went yesterday and last night I reverted to the old nasal unit BUT this time I also used a special mouth guard designed to stop snoring. And the result this morning - a smiley face for no leaks and an AHI of 0.3

As posted before it is now obvious to me that the CPAP machine achieved nix when I was able to bypass it and breathe through my mouth. Hopefully the F20 will work. And it seems the F30 gives leak problems for others also. If it works for you - terrific, but if you are looking at getting as full face mask, be warned.
Getting used to CPAP gear is challenging at the best of times but having a mask that leaks means that "sleep" ends up worse than without the breathing "assistance". So, if you are having leak problems, look for a different mask and I repeat, make it a full face mask or like me, you will curse CPAP as useless and not feel better using it.