Disclaimer: Do this DIY at your own risk. Not responsible if your trans fails or you get injured.

Car: 2006 325i Step Auto 49,300 miles (I have a ZF trans., check posts 73 and 74 to see if you have a ZF or GM Trans.)

Materials:
6 Quarts Castrol Import Multi-vehicle trans fluid ($4.50 - $5 a quart) (See attached spec sheet).
1 clean bucket ($1 store)
Transfer pump: $5.99 at harbor freight
4 quart drink container ($1 store)
Digital thermorter ($3.12 Walmart) I didn't use it (will explain later)

Tools:
3/8" ratchet
small extension
8mm socket
8mm allen wrench
10 mm allen socket
Any size wrench (I used a 17mm) (will explain later)
4 jack stands
1 Jack
Goggles

Instructions: (Again, at your own risk)

1) Jack up the FRONT of your car 1st and place jack stands at the jacking points on the sides of the car. (Rear wheel drive, therefore must jack up the front of the car first.)

2) Jack up the rear of the car under the differential (Not the cover) and I wouldn't recommend doing it under the cross beam, it looks sturdy, but BMW doesn't mention this spot as a jacking point.

3) Using the 8mm socket remove the transmission under-cover.

4) Using the 8mm allen wrench and "any size wrench" (I used a 17mm wrench) open up the fill hole (see pic). The "any size wrench" will give you leverage. This would be extremely difficult without the extra leverage. You may also want to use goggles because my allen wrench was bending when I applied force (I thought I was going to break it!). Also, there is no space for a socket and a ratchet. Further, place your oil-catch under the fill hole because a lot of oil spilled out of the FILL hole. That shocked me because how am I suppose to fill it up when it was GUSHING out the FILL hole. I figure it may have to do with the temperature of the oil.

5) Using the 10mm allen socket open-up the drain plug (see pic)

6) Place the used oil in the container to see how many quarts came out of your transmission. 4 1/4 quarts came out of mine. I know, I know, what about the torque converter. Something is better than nothing. Plus I plan on doing this every 20,000 miles so the next change or so should get alot of it out. (Castrol recommends 15,000 to 30,000 miles changes). Besides, its lifetime fluid so who cares about the fluid in the torque converter.

7) In order to do this job on my own I filled the dollar-store bucket with 6 quarts of oil. 6 quarts because the transfer pump hose will have problems getting the fluid at the bottom of the bucket; the hose tends to curl.

8) With the drain plug back in the trans, start pumping fluid back in the trans. until oil starts spilling out of the fill plug. See pic. You may want to cut some of the hose length of the transfer pump (those hoses are long). I cut about a foot off each hose.

9) Re-install he fill plug and start the car. Shift through the gears slowly WHILE PRESSING DOWN ON THE BRAKE (ie: P->D wait, D->P wait, P->R wait etc.) You might see a symbol of a car with arrows pointing in both directions. That is just a warning that your car may roll because the parking brake is not engaged

10) After about 8 minutes (you do not have to shift through the gears all this time), with the car still running, I placed my hand on the transmission pan, it was warm therefore it should be between 86 -122 degrees F. I opened up the fill hole and no oil was coming out.

11) Here is where you may want to insert the temperature gauge in the fill hole. I forgot to do this because I was nervous that my engine was running and I know the trans was low on oil. But at least I knew how many quarts came out of it.

12) Fill the trans until oil comes out.

13) Re-install the fill plug, re-install the trans cover, jack the car down, and you are done!

Overall experience: The oil was golden yellow to black and it contained some gray matter (friction disc material). I used about 4 1/2 to 5 quarts of oil. The car feels exactly the same; which is a GOOD thing! I plan on doing this every 20,000 miles (that is why I went with Castrol, cheap and it specifically lists our spec.). Assume everything is fine unless I give an update here. I plan on changing the filter next time around. Good luck.