my s1 had the same problem the backs of the subframes crack and split, if you remove the seat split the top from the bottom then the bottoms are pretty easy to strip down, theirs not much to it at all then just straighten the frames up weld them bit of paint to finish and thats it put it back together and jobs done, it took me bout 1 hour to do the drivers seat, when its back together you carnt see the welds either