Recommended Fluid
WARNING: This page is about a different car, the 2005 BMW 530i, 2005 BMW 525i, 2004 BMW 530i, and 2004 BMW 525i. However, it is still accessible from the selected car via links, so may be relevant.
Transmission fluid has a condition based service interval of approximately 100,000 miles. Never mix any other oil with this transmission fluid when doing repairs or topping off. Use Shell (M-1375.4), BMW part No. (83 22 0 142 516).