Great write-up! Thanks for posting.
I'm getting ready to tackle the B1 S1 sensor in my 07 Wagon. Would you say B1 S1 is much easier to get to and complete the job?
BTW --- $55 for the O2 sensor, Genuine BMW part --- what a deal!!!
Now, the part sells for $140+ (Bosch) and $200+ (Genuine BMW).