I would do all 4. Is the same type. Even if they are not original, they must be getting old. 4 of the Chinese mag ride replacements. Should not need sims. If you module is good. I would do that. Mag ride does deliver a better ride for the Cadillac. If you want to go standard struts, do all 4, you will need a sim kit. 8 sims total. 4 for the struts and 4 for the ride height sensors. Mickeytee can suggest which strut gives the best ride that's a bit more luxury and not too aggressive. I live in PA. The roads suck. I have the b8 and they handle great. But I can tell they are not as smooth as the mag ride. I would have preferred a lil more luxury and a lil less sport. It's an XLR, not a Vette.