I just had my 73 450sl subframe repaced by a dealer today. (I pick it up tomorrow.) I verified with MB that it had never been done before; so I think the dealer can tell by the vin number if it has been done or not. I didn't need the bushings replaced, as I had those done a while ago. I did have the lower ball joints replaced, however, at a cost of about $300.00. I think this is high, but I went ahead with it anyway. I think the replacement of the subframe bushings is a lot cheaper, maybe about $100.00.