I replaced the gearbox and diff oil today.
Wasn't too difficult - only because I'm starting to get more comfortable going under the car again.
I used redline d4 for the gearbox and redline 75w-90 for the diff.
I used an old bottle of hand wash and attached a small tube to the end with a clamp to secure the tube in place, filled the bottle of hand wash with the above oil and then kept pumping it till some of the fluid started to come out the filler hole. This is the only clean method that I know the only downside being that it took a very long time to pump all the fluid out., 10 minutes of constant pumping for the gearbox which took approximately 1.3 and a similar time for the differential.
I couldn't find a 14mm hex bit on a socket anywhere. I was tempted to use a bolt and two nuts with a spanner to remove the diff plugs, however I ended up buying a set of hex bit from machine mart. Annoyed cause I only needed the one but had to buy a set! However there's no way the bolt method would have worked as it took a lot of force with a breaker bar and a half inch socket to break the diff plugs loose.
To be completely honest I've not noticed any difference yet in the way the car goes into gear.
My differential fluid was the cleanest looking fluid I've ever seen come out of a car. It looked like really clean oil, almost as clean as what I put back in. Does this suggest a recent change or that diff oil doesn't get as dirty as engine oil.
Old Transmission fluid was also a nice colour but not nearly as clean as the old diff fluid.
I didn't have any history in regards to transmission and diff fluid changes and the last big bmw inspection - inspection 2 for this car was done in 2007 so I did it as a precautionary measure more than anything.