John, just as a comment; I have discovered some obvious quality/longivity differences in some of the aftermarket replacements; particularly the motor mounts and control arm bushings. I've seen the cheapy motor mounts sag out in 2-3 years, and control arm bushings collapse much quicker than OEM.
Of course, even my MB dealer sells non-OEM parts sometimes, so it's hard to know what you're getting these days.
DG