I have a 2.2 auto box here you can have it free of if it helps mate
There is also one on my spares car you can have for free, although the 3rd gear solenoid has gone, but it does have a new filter. I was having the same prob as you
What was wrong with yours in the end phil, if you don't mind me asking?
Very interested in the filter proposition also 
The box (and filter) are still on the car on the drive
You will regret asking

I was having similar probs as you, not going into, or banging into 3rd gear, limp home mode, auto box error on display.
Did the filter and atf change and saw some improvement but after a while it came back. Consensus on here was that it was 3rd gear solenoid.
Came up with a "put me on" solution until i could change the solenoid.
When it didn't change to 3rd when i expected i would put into N (for a sec) and then back into D and it would re-engage in 3rd and drive normal, changed down and even kicked down. Just going
up to 3rd was prob. BTW prob seemed to almost go away during the winter

As you would expect this solution "put me on" for quite a long time (about 6 months) and then about 3 weeks before I was due to go on holiday (in car) it stopped being a solution, played up in other gears and started to do other things as well as throwing up cam sensor codes. I played with the thought that it might be because it was summer and warmer

Anyway out of curiosity looked on the bay and found the one I have now for sale and managed to get them to drop price by a grand and bought it. Holiday sorted and deal with the problem when I got back. Which I put off and put off (1 year) until eventually decided to just strip the car for spares.
Told you'd regret it
