This thread is beating a long dead horse, but perhaps it's still an interesting discussion with some very valuable information. Let me just interject a couple of my observations/concerns:

1. I think there is certainly some strong credibility in the don't change the fluid in a non-maintained transmission, the question is, just what constitutes a properly maintained transmission where one wouldn't be at risk, or at least significantly lesser risk, of dislodging sediment? IOW, what's the magic cut-off mileage or age? Regular 10,000 mile changes, 15,000 mile, 20,000 mile, yearly, etc? With this I think I'd be more interested in hearing from ZF than BMW.

2. Given that BMW specifically states lifetime fill on the transmission, one concern I might have is that if I did change the fluid, and something went wrong with the transmission, would they cover it under warranty since they specifically said not to mess with it?

3. Not to add a 3rd component into the mix (engine oil, transmission fluid, and now...) but beginning 2004 model year BMW suddenly went to lifetime fill for the cooling system. Marketing decision? Does it fall under the same circumstances as transmission maintenance, etc?

4. While BMW seems to be gradually moving to completely maintenance free cars (at least on paper, especially when you are on a 3 year lease!) it appears that as newer engines come into play they are stepping up some maintenance schedules. Here is an interesting list of the 2011 model year maintenance schedules just as an FYI...

For the 335is (Coupe and Convertible), Z4 sDrive35is, and 740i/Li with the N54T engine:

• There is no 1200 Mile Service.
• Engine oil is the same as for the 335i (recommended: BMW High Performance 5W-30 Synthetic oil P/N 07 51 0 017 866)
• Spark plug replacement interval is 45,000 miles or at every 3rd engine oil service.
• Engine air filter replacement interval is at every 2nd engine oil change.

For the 135i (all versions), 335i (all versions), and 535i with the N55 engine:

• Spark plug replacement interval is 60,000 miles or at every 4th engine oil service.
• Engine air filter replacement interval is at every 2nd engine oil change.

BMW ALPINA B7:

• There is no 1200 Mile Service.
• Spark plug replacement interval is 30,000 miles or at every 2nd engine oil service.
• Engine air filter replacement interval is at every 2nd engine oil change.

Vehicle check: Check the expiration date on the M Mobility System sealant bottle. Change the bottle if needed.

ActiveHybrid 7: Maintenance is comparable to a 750i.

Spark Plug Replacement Intervals

2011 Model Engine Interval (miles); coincides with every _ Engine Oil change

128i, 328i, Z4 sDrive30i N52TU 60,000; 4th

135i, 335i, 535i N55 60,000; 4th

Z4 sDrive35i N54 45,000; 3rd

335is, Z4 sDrive35is, 740i N54T 45,000; 3rd

M3 S65 37,500; 3rd (first oil change is at 1200 miles)

550i, 750i, ActiveHybrid 7 N63 60,000; 4th

760Li N73 60,000; 4th

BMW ALPINA B7 N63B44M1 30,000; 2nd