[Soravia]

GSP brand rear axle shafts I bought were for older 325i series, even when I sent VIN to seller on eBay. Too small to fit the xi and 330i/335i/xi bigger splines in wheel hub.

I ended up buying used E92 335xi Automatic rear axles with low miles.
All 328xi / 328i xDrive (Auto and Manual) share rear shaft with AWD 335xi 335i xDrive Automatic (Only) rear axles. No one sell those new aftermarket in USA.

UPDATE: E91 E92 rear axles, even LCI will not fit the hubs on E90 E91 LCI. Splines are just different.
Check on RealOEM.com for hub compatibility. I think most of the shaft inside part to diff are same, and if inside diff flange, and the outside wheel hub are the same between the cars, the rear axles will fit, with small difference in shaft size to handle power from turbo engines, etc.