I believe you have to remove the lower bolt of the shock in the rears to enable adjustment of the separated spring. It is recommended to replace that bolt when removing it. There were some instructions in the copy of the manual hosted on newtis, but it looks like BMW forced them to take it down
Bummer on your fronts, mine rotated smoothly but my car also had sub-1k miles when I fiddled with it. Curious if the threading on the coilover body was damaged. I've had no issues with dirty racecar perches that couldn't be solved with brake clean, a brush, and compressed air.