e60 535i N54 Transmission swap? Fix?

[Kaikun]

Hello,

I have an 08 e60 535i with the N54 motor and 6hp21 transmission drivetrain. The transmission is on its way out finally after 200k miles. I did service the transmission replacing the seals, fluid, and pan but that didn't really help with my trans slipping and not holding gear when getting into load. I think the clutches have finally worn out after its long life. I have been trying to do some research on replacing the transmission but I am a little stuck on what to do.

Obviously the easy route is to find a used transmission from another same model car and put it and do the necessary coding. From what I have also looked into, some people say that you need a new mechatronics(valve body) since they are locked to the car? Or if I just use the mechatronics that Is in my car right now and swap it over to the "new" transmission.

I know that the 6hp21 is in multiple models of cars and there is a 6hp21 from a 08 530i that has the M54 motor in my area which I could possibly get for stupid cheap. Is it possible to swap that trans in and code it or swap mechatronics?

Of course the newer f30 model 3 series also have the 6hp21 bolted to the N55 which the n55 is basically the same as a N54. I was told by BMW techs that it won't be possible to use that trans due to coding issue.

The other WILD idea is that an 8hp swap could be done with a 8hp45. But of course that requires to use a standalone TCU from like TurboLamik. But that is a lot of money and work. But any info about this could also be helpful to my curiosity bug.

BUT if any help and knowledge on the easiest and budget friendly way to go about replacing my transmission would be super helpful. Of course I am trying to save money in any way possible.

Thanks!