BRE used detroit lockers with the R190s that they ran in their cars.

Yes Jon, I would expect that if this part was used before that the owner would know what he has...however you can never tell....

I erred on the side of caution and pulled the diff out and took it to an expert. It turned out the diff is fine, but that the half shafts had been over tighten, causing the clutches to lock. The Diff mechanic said he has seen it once or twice before, and chamfered back the ends reset preloads and seals.

Can't help thinking if I had c/o the diff myself this wouldn't of happened, either there was a tiny difference in the 240z half shafts or perhaps the mechanic who fitted the diff used a rattle gun !