Hi Mick
Your photos look nearly there, that scum IS the oil forming.
The second part of my recipe=
To finish it off, you can do it two ways, but either way you have to thin it down with plenty of water.
1. Quick way is to bring it back to a rolling boil with a lid on, important that you give it a stir
every few minutes as the onion sediment gathers on the outer edge at the bottom of your pan
and can overcook. The trick is that the oil will separate and be carried up with the steam. If you
check inside your lid, after say 15 mins, there should be little droplets of oil stuck to it. How long you boil varies,
but once I get a scum forming and an red/brown oil slick around the outer edge of the pan, I turn it down to a simmer and then off.
2. The slow way, is to bring it to the boil then turn down to a low heat simmer, give it a stir
now and then, until you get the scum/oil. ( always keep a lid on until you get the oil)
It doesn't really matter if it doesn't release loads of oil, as once you've scooped most of the scum off,
you should give the pan a good stir and the oil will mix back in.

Cheers Chewy