If I shake my rear tire back and forth (sort of like checking wheel bearings on the front) I get a lot of slop. Something tells me this isn't good and my rear diff may be about to die. I currently have a '91 RS with the stock non-posi rear. So question is, if the rear does go out, is it easier to buy a replacement used posi/disc setup from a wrecking yard, or is there some kind of LSD module that I can just bolt up inside the stock diffrential housing? I've not played much with rear diff's so any help would be great!