If the box is still working normally with those miles I would be considering dropping the gearbox and renewing/refurbishing the torque converter. TC is the known weak link in this gearbox and when the locking clutch surface wears off metal debris will very soon destroy the rest of the box.
If you are going to change the oil why not flush change the whole content. You can do this by disconnecting the line going to oil heat exchanger. Guiding the fluid from there to a a drain reservoir and filling the oilpan with drill pump or similar while engine running. Dexron III -H is the specs. I've used Petro Canada ATF D3M.
Here are some pictures from 2007 when I did this first time to my E39 530d with the same gearbox. It had a new TC at about 300t km (preventative) and now running 400t km without a problem.
https://photos.google.com/album/AF1Q...5o-PwXajFVf-pc