Okay, not great news I'm afraid.
Gearbox emptied, bank 3 solenoid changed with a delightfully expensive substitute, re-filled, cycled, level checked again re-assembled.
Still getting the notchiness although I might say that it is a little better (perhaps notchiness isn't the right word as it appears to be more hunting up and down the revs (100rpm up and down)). When I approach a junction now, the kick down to 1st feels more severe somehow; certainly more so than it did before the service.
Reader is showing no fault codes whatsoever now though so may have cured one issue but not them all. It doesn't change gear when it 'hunts' at low speed, the revs increase and decrease by about 100rpm. When I select the gears, it does as it's told, kicks down great and when I 'boot' it, it's fab. At 70mph on the big roads with the cruise control on, it's flawless, so it isn't gear specific as it will do it in any gear providing the revs are low enough (sub 1800rpm thereabouts)
There is also an irregular knock when in park, not sure if this is related. Don't think it's the bottom end as it doesn't do it all the time.
If it was a wiring fault, I'd expect codes; is it possible that the TCM (despite looking okay) could be on it's way?
If it's the gearbox itself, then I'm afraid it's curtains for the old girl; can't afford to keep throwing money at her.
Let me know what you think if you can; I appreciate the additional support. Don't want to consign her to the scrap heap, she looks too good for that!