Finally got round to having my auto box oil changed, £100 all in at 'Tameside Transmissions'
http://www.gearsandclutches.co.uk/It seems to change gear better and run better unless its in my head.
142,221 miles the car has done so it was probably well overdue an auto box oil change.
The reason I had it done was; it needed it doing due to the mileage, and when slowing from 30 either 3rd to 2nd or 2nd to 1st somewhat banged in to gear.
After the oil change and a 10 mile drive around town to see if it would do it again it only did it once (maybe the oils not got round yet).
I'll give it another go today to see if it still does it.
If it does then I am open for suggestions to what is causing it to 'bang' when changing down. On 'one' occasion it point blank refused to change up a gear and did after a while and banged in to 2nd gear. To be honest maybe I confused the auto box due to the driving stile at the time and going down hill then up hill.
Rear diff could be on the cards as the next option as it looks like the rear seal has gone (no major leak though).
http://www.omegaowners.com/forum/YaBB.pl?num=1161520937and to be honest the bang sound seems to come from the rear and not the centre where the g/box is.
:-/