go here...
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and search for "kirt" or post your prob there... best site for that issue. Kirt is the tranny god of the 540, he will set you up. call him directly, his # is there. he sells parts and will give you the info you need. reach me at sharkmanbmw at hotmail dot com
I had my valve body rebuilt for $700. DO NOT FLUSH OUT THE system whatever you do. change the filter and any oil that comes out during that procedure, refill and go. if it still is not right, then you have bigger issues.
did you get the "TRANS PROGRAM" error??? if yes, that is whgy the car is slow, you are stuck in 3rd gear whenever it says trans program.
go to bimmerinfo and post, there is a 540 every week with the same probs.
it could cost you less than 1000 if you get to the right place, thje dealer will ONLY replace it. They don't know how to fix anything, just swap parts until it works!
If you only add fluid and it works, be grateful!