My 328 arrives in a month but I decided to be safe and went by the dealer and had my daughter put her booster into a similar car and buckle in.
It did not go well.... The booster covered the slot and she had issues reaching all the way around to get the belt in.
I had similar issues with my TL and I bought a seat belt extender. I then went to the same place I bought my other seat belt extender and saw this:
http://www.greatravelstore.com/seat-...-window-seats/
Uh oh... So what are the parents of this forum doing? Is there a different booster that is more narrow and doesn't cover the seat belt slot?