Hi! they are probably talking about the mechatronics sleeve which is fairly common, plus many suffer from cracked plastic pans, so you replace everything in order to reach the sleeve so you have to take the trans pan off, then most will change the fluid, at least 5-6 litres.
There are a number of threads with a really good DIY on the E60 forum and another on the E65. The leaks are very common across the range of BMW cars now.
Does my bum look good in this !