Also changed the small plug in the oil galley underneath the rear casing for a plug with a proper copper seal. Much easier to check the oil flow this way.
And to finish work on the gearbox for the time being I measured the end float on the bearings for the mainshaft and the layshaft. It always looks quite easy but in the end it took me well over an hour to measure the end float on both shafts. The layshaft turned out to be spot on, but the main shaft needs a substantially thicker shim. So now waiting for that to arrive!