Greetings everyone. I am a new member and this is my first search for information about my 2004 330xi automatic, as well as my first post. I recently purchased this car (from a BMW dealership, it was a Certified Used trade-in) and decided to begin the process of checking it over before winter, as well as maintaining the consumeable maintenance items such as: oils, filters, fluids, etc. I know from my experience with my 2001 E39 530i automatic that buying the "original" BMW fluids can be very expensive, and that finding the best alternative requires research, and then a decision based on a price comparison and a belief that the "non BMW dealer original" fluid will be an adequate substitute.
When I asked the local independent BMW repair technician the question about draining and refilling the transfer case on the 330xi, he replied that I must use the original BMW fluid that that is sold in 1 liter bottles for about $60.00. It was after this discussion that I began my research, which included this forum. I would like to share my experience and decisions.
When I recently drained the transfer case, the odometer registered approx. 85K. I do not know if the fluid had ever been changed. It was very black in color. IMO, it was thinner than "gear oil" and thicker than Dexron. I read every post in this thread, and followed many of the links, and this is what I decided to do. I refilled with an inexpensive Dexron for a quick flush. I drove it for about 50 miles, on dry and wet roads, and did not notice any change in performance. I drained the Dexron, and it was a very dark red color now. Obviously the Dexron flush removed more of the old black fluid. While I was at the BMW dealership buying more of the copper sealing ring washers for the fill and drain plugs, (at only 24 cents each, list price, why not!) I inquired about the type and cost of the "factory original" transfer case fluid. The parts man asked for the VIN and then printed a single page BMW document titled, Operating Fluids-Transfer Case, dated September 2011. It listed the E46 325xi/xit, and the 330xi, as well as all models from the E30ix all the way through the F25 vehicles. As listed, the "approved" fluids are: E30, Dexron lll. E46(all), MTF-LT-1 (now MTF-LT-2). E53 with NV125 transfer case,Dexron lll. All other models to present, use TF0870. I asked him the cost of the BMW MTF-LT-2. He replied that the BMW list price for a 1/2 liter of BMW MTF-LT-2 (BMW part # 83 22 0 004 008) is $15.42, my cost as a commercial customer was $10.10. He then filled a new, empty container from a 5 liter pail of BMW MTF-LT-2, and said that he would give me enough fluid to drain and refill the case twice. I refilled the transfer case, spun the shafts by hand several times to disperse the fluid, confirmed that I did indeed have enough fluid to drain and refill again. IMO, the new, original BMW MTF-LT-2 fluid was thinner than "gear oil" and thicker than Dexron. I drove the car several miles and rechecked the fluid level. It was still full.
To summarize, I purchased enough of the BMW original transfer case fluid from the BMW dealership (and enough copper sealing ring washers) to drain and refill the transfer case twice, for less than $11.00 my cost, less than $17.00 list price. I plan on performing this transfer case fluid service again in about a year.
I would like to thank the authors of the previous posts for sharing their information and experiences.