its definitely a s1 box cos a s2 wont fit..unless the internals had been swapped by the previous owner..it behaves like an lsd should..i will try jacking both sides up and if it turns more freely i take it it must be ok..i park it on a bank and it freewheels down the bank so nothing sticking..was more of a concern that something was on its way out and end up stuck in the middle of nowhere! haha