Happened to my 2002 M3. I took it to get reinforcement plates welded on the subframe and had them do the subframe and differential bushings. I was told that one of the differential bolts was messed up and destroyed the threading. They drilled out a bigger hole and put in an insert but the guy says it can only be torqued to 85 lbs. The differential bolt is supposed to be torqued to 128 ft/lbs. Any thoughts on if this sounds right? Would there be any other way to fix this? His other option was to get a used differential and swap them....

I can't speak for the torque valve, but my bud has an e46 m3 and had the diff bolt strip. He drilled it out and tapped it to a larger size. It lasted for a while before it broke again and he swapped in a used diff.