Very nice, Paul - that's a late-production U43 with plastic motion, pickup skates and the gold-rimmed lights, isn't it? The earlier production of the same loco (metal motion, smaller lights and no skates) is a rather different procedure as it's the old type of split gearbox, but actually needs a bit less disassembly than your newer one.
I can post a couple of pics of how to do one of the old type if anyone is interested?
Jon.