Here's the pelican write up for the E90. Should be extremely similar, I know on my 128 there's enough room to get in there without dropping the exhaust or driveshaft. It's cramped, but doable.
https://www.pelicanparts.com/BMW/tec...eplacement.htm
Common practice on older BMWs was to install a new seal on top of the old one, you can just hammer the new on one with the 15mm socket and it will push the old one deeper in the bore. But you can only do this one time, I did it on my E36 and Z3 and it never leaked again, has anyone done this on the E8x/E9x?