As all of you who are regular participants on the board know, there is has been a great deal of discussion on this board, and the e34 board, regarding "maintenance free" automatic transmissions. I have posted several times that while I was surprised at the owner's manual claim that the fluid transmission is lifetime, backed by my dealer's opinion and that of a trusted independent I advocated leaving the unit alone.
I seem to have been fortunate in the fact that the transmission on my car is smooth and trouble free. However, recently, I noticed a slight increase in the unit's noise level when shifting, a noise that was not present when the car was cold but only when it was warm. I suspected the fluid because the noise was temperature dependent--so I guessed it had something to do with the oil's viscosity.
I then proceeded to call a few Roundel tech advisors, and their advice was unanimous: change the fluid. So I made an appointment at a local BMW shop, and $300 later (the fluid costs $135, 1.2 hours for labor at $68, a $50 filter and $25 in miscellaneous stuff), here is what I can report:
The transmission shifts like glass. Not that it was bad before, but it is absolutely perfect now. Further, all noises have disappeared and the shifts are perfectly quiet, except for the burbling made by that great v-8.
So in sum, I would advocate for all the "maintenance free" tranny owners out there, whether 3.0 v-8, 4.0 v-8, or the one that appeared on some '95 525 and 325 models, to changed the fluid, with one caveat: make sure that you have a shop do the job that knows what it is doing, as if you do not, they can destroy or damage the transmission. If you find such a shop then definitely have it done. Also, the mechanic I spoke to said if it were his car, he would change it every 60k (this sounds more reasonable as many new cars have this interval), and if you drive hard, every 30K.
My next task is a letter to BMW NA asking them to change their position on the maintenance free nature of the transmission. I will let you know how it goes.