Ordered my hitch at:
The 2011 fits perfectly on my 2012. Followed the directions:
1) removed screws holding on difuser
2) pulled off difuser
3) mounted hitch, (not sandwiched), bolted down with 19mm socket
4) put difuser back on, re-install difuser screws
No vibrations. 30 minutes. Fits perfect. Thule 4 place bike rack installed. I love it! No bikes near or on my car. No garage height issues. Truck accessible.
Happy 2012 135i owner.