OK, all done and i'm back home!
I didn't get to see any of the work that was done, frustratingly, but all they had to do in the end was replace the bearings on the front-right wheel and top up the transfer box oil.
So... the swivel ball isn't too corroded. it's mostly just surface rust with baked on dirt. Wire wool or a nylon scouring pad should solve that.
The transfer box needed 2 litres of oil. Is that a lot? It's not leaking anywhere, so I suspect it's not been topped up for years!
They mentioned a slight oil leak engine or sump. I know about that anyway, and i've not had to put any oil in it since i bought it anyway, so I guess it's minor at this stage. The previous owner told me he'd had the crank seal done (which commonly fails on the 300Tdi, i'm told). There's a fair bit of oil around the rocker box cover too, so I actually suspect it's finding it's way down from there. Let's hope so, anyway.
They also checked the levels on the entire underside of the car. this, i guess, included the diffs, swivel balls, transfer box. Presumably that's it. The auto gearbox and engine are done from up top, and I know they're fine. They also greased everything that they could grease. As I don't have a grease gun, and don't know when any of the prop shafts, UJs etc... were greased, I asked them to do all that too.
They also gave it a pre-MOT check over and said everything looked fine and the Landy was in "good shape"!
They did point out that my rear brake pads are low and my O/S/F side lamp is broken, but the bulb should be 5 minutes, and the brake pads around 15, maybe?
Anyway... the old bearings were knackered. The outer bearing was OK, but the inner bearing had pretty much disintegrated, hence the squeaking. My adjustment attempt was perfect, I was told, and that I'd done it exactly as it should be done. I was, however, nipping up a disintegrated bearing, so not ideal. Here's a few pics of the old bearings (which I asked to have back!)...
Overall, it was 2 hours work for just under £220. A lot of money, but I know the vehicle is happy now.
So... thanks for all the help, people!! Next time this needs doing, I'll know how to do the adjustment, at least, and can also teach someone else now!