Took the 12 bolt out of our "Formal" Chevelle down to the local Axle Shop to have a posi unit added and a 3:73 gear set installed. They charge $85 for tear down and reassembly..'nuf said? Part of the process is to check the housing for straightness in relation to the axles and axle bearings. They install a tool that is torqued in place of the center section which makes it easy to see if the tubes are centered. Long story shorter, had to have the housing sent out to be straightened before reassembly can occur. Do you guys in the rear axle business see a lot of this?