Wow, my gearbox is much more quiet now!
My local BMW dealer just finished replacing the gasket of the mechatronics unit and a cable harness which was also leaking oil... They also flushed the gearbox with Pentosin BMW-DCTF-1, SAE 75W.
The small ticking sounds that I used to have before each gear change when fully warm are now completely gone.
Again a big thanks to Jannisa for recommending having BMW check the car for new leaks!