I have a 09 328i that I purchased new. Had the rear bushings replaced by the dealer (under warranty) at almost 50K miles. Now have almost 89K miles and my mechanic says these are cracked and leaking again. Also need rear shocks because they are leaking. Is this normal wear and tear on a 3 series? I have a neighbor/mechanic friend who can do the work for me. Should I get BMW parts??