Hopefully this is a helpful fix post to anyone else having the issue of a gearbox that sounds like a bag of spanner sand bad selection (if any)...
Before you spend large sums, check the injectors...Specifically no5 (on a D5)
A week ago I changed the swirl flaps which requires the removal of pretty much everything around the rocker cover, inc the injectors.
Everything was running smoothly afterwards(best its run in a while) and then, just after joining the A1, at a steady speed, the dashboard lit up like a Christmas tree and the car lost power and I only had 3rd gear, limped home (18 miles took nearly 2 hours..)
All the journey home I only had 3rd and the car shook when setting off (which I tried to avoid as best as I could).
All indications were a broken gearbox as I only had reverse and when put into drive, it jumped straight to 3rd gear.
I plugged in VIDA this morning and it showed TCM faults but it also showed communication problem to No5 cylinder. The engine didn't seem like it was mis-firing though.
I opened up, checked No5 and sure enough, the connector was about .5mm out of the injector, just off the retaining lug ...
I unclipped it fully and pushed it back on, cleared the faults on VIDA and re-started the engine.. All faults cleared and could select any gear and drove without any fault !
If any members have any idea why a loose connection on an injector can cause such severe gearbox issues I'd be really happy to know.
I mean, if I had severe tooth-ache and it went because I clipped a toenail.. you'd want to know why, right ?
Hopefully this will help anyone else... Sweating on the A1, in limp mode, stuck in gear, with 3 dogs, the missus and your eldest, on the way to Scotland...
Cheers Gents