I have noted the comments about using Dexron VI and raised it with the Caffyns main dealer parts manager.
However, he has assisted me for 18 years with GM / Vx parts and is very familiar with the Vx Omega, as many of those used to go through the servicing department, and he had to organise the supply of parts. He has assured me this morning that Dexron III has been superseded by Dexron VI within the existing, ex GM range, now recommended for my car. He is adamant that this is so, and indeed very suitable for my particular Omega, and even beneficial for it.
I have to say this is backed up by information on line from the stockist of these oils, with comparisons of the two products, such as on takeuoil.com/dexron-3-Vs Dexron 6 who specify that unlike Dexron 3 which " is a fully synthetic fluid", Dexron 6 "is a blended synthetic oil" and ".... "is specifically designed for old GM vehicles".
In another general reference on-line it is stated, in answer to "is dexron VI compatible with dexron III power steering?" , "....Yes.
DEXRON VI licensed fluids are fully backward compatible and can be used in all applications covered by earlier GM ATF specifications".
So, although of course I respect the opinions of the Omega specialists on here, I cannot ignore all this latest information about Dexron VI. I will therefore be draining the power system system of whatever is there (which I am not sure of anyway!) and filling with Dexron VI.
If my rubbers start deteriorating.....oh, well that will be the end of my twenty year old jalopy :'( :'( :'(
Once again, thanks all for your advice