There are a few recorded failures, one in particular is on YouTube which was catastrophic, the gear box bearings came apart. The only way to change oil in the rear diff is to suck it out. BMW states the lube is lifetime. What I did on my 4.8 is squirt a tube of LubroMoly antifriction for gears for insurance and to keep it cool and quiet over the long term. Differentials get hot, especially in the South and they do fail over the long term if not cared for, especially with 360 horsepower driving them.