I am not going to do anything until the 100K change but want to estimate the costs for my maintenance spreadsheet. I will have the dealer or qualified facility change the ATF and replace the filter at that time.
I plan on keeping my 325xi for at least 12 years. I had a Nissan Pathfinder for over 16 years when I lived in Colorado.
I have determined that my 6spd Steptronic is a 6HP 19 made by ZF (Actually GA 6HP 19Z from the realOEM wbsite). The ATF is Shell M-1375.4 (BMW part # 83 22 0 142 516). I estimated that it takes 6 liters based on the other BMW transmissions.