I am going to put as low a mileage unit as I can find. Use my rebuilt valve body and egs (egm? Whatever BMW calls the mechatronics computer) in the replacement. Going over the tis it doesn't look like too bad a process, but requires some special tools, and will be tedious. Perfect way to spend a couple weekends.
Then, at my leisure (or maybe not? Life gets in the way, our house is a constant source of projects) I'll rebuild the old trans and replacement valve body. I didn't rebuild mine because I did not have a spare.