"The main transmission shaft is another technical highlight of the 9G-TRONIC. First, at 550.9 millimeters, it is one of the longest shafts in the entire automotive industry. Second, it performs other functions in addition to its main purpose of power transmission: using a sophisticated internal ducting system, the shaft also performs various lubricating, cooling and control functions."
It's easy to guess what happens with this kind of systems with "lifetime" fluid. Channels get blocked with dirt coming from the clutches, and eventually everything falls apart.