check you alignment.
Too much toe will accelerate the normal proclivity to wear the outside of the front and the inside of the rears.
Report the toe numbers on all 4 wheels. DEMAND that they set the to to 0.01 to 0.03. BMW allows up to 0.08 on each or a cross toe of 0.16, WAT too much
At 23k miles you are no getting horrendous wear, so I dont expect grossly bad numbers....but I bet it could be optimized for wear.
Keep it as simple as possible...but no simpler.