By way of an update, we've taken people's advice about the gearbox and Bearman has kindly built us a shiny new one. My garage space has always been a bit tight, but we might have just bought a new place with plenty of room for spanner wielding and gearbox wrangling. Assuming that all goes through, the box swap will take place and the rear main will be investigated. At the same time there will be a long list of things to do that make sense while it's all apart. The trick will be to not allow it to turn into a three year rebuild. We've all been there.