Well, I have got it all back together now. Was too dark to take any pictures outside by the time I finished at 9pm so I only have a couple from installing the new gearbox insert.
It also seems to run much quieter now, with this new insert. I have only taken it around the estate as I had to use my phone as a torch to see where I was going. Will take it for a longer run tomorrow and adjust everything to eliminate any untoward noises & squeaks.