I'm just getting done going through this as well on my car. Most bizzar thing ever...
Bought my car with 47k mi on it from private seller. Had new tires on it. Put 7k miles on it and the rears were showing wire on the inside. Same thing with the new set. I'm 20k miles in and on my 3rd set.
I got my rear end out from under my car and found that one axle slid out really easy, while the other axle had to be hammered out, which proved to me that the housing was bent, since the axles were fine.
I found a rear axle near me with relatively new 373s for $50. I stripped it (to have it repainted and bearings gone through) and noticed that one was bent as well. So I took those 373s, bought another rear axle from a local mechanic, and out the 373s in that rear end, with all new bearings.
Needless to say, I'm ready to be over this mess. My mechanic should be getting my rear axle to me soon and I should be able to drop and replace my current rear end over a weekend. Other odds and ends are connecting the dots for me: the previous owner abused the heck out of my car in it's 47k mile lifespan.
Also, I don't know how your going to check the straightness of the rear end. I think it's nearly impossible as there is so many places a bend could be. It's literally the only thing that could cause the uneven tire wear on these cars. I would just recommend finding a used 8.8 rear on Facebook or Craigslist, they are all over cheap. For the most part if 8ts coming out of a decently low mileaged car, you wouldn't have to worry about stripping it unless your anal like me. Good luck!