I’ve put a ton of work into my 2011 BMW 128i. Recently, after installing a factory-sourced horsepower upgrade, a limited slip differential to get the rear tires to grip harder, and more stopping power ...

So you bought a 335i, because let's face it, they are a performance and luxury bargain, and you want to modify it, make it faster and improve its handling. But BMW never offered a factory limited-slip ...