[projectRDM]

That is an early J30, the 5bolt output shafts and finned cover give it away. Later J30s look just like the S14 diff, 6bolt with a flat cover.

My question is, how did you get ripped off? It's the same exact unit as an S14 VLSD, which is the same in Japan or the US. In fact, the larger cover has both increased cooling and oil capacity, both of which you wouldn't get from any S14 diff. Only the later J30t models have a different gear ratio, that's a 4.08:1 just like your OE diff and any S14 diff would be. Plus you get the benefit of buying a diff that's been gently driven in an automatic luxury car it's whole life instead of beaten to death from sliding into guardrails and ditches from a JDM car. Aside from needing 5bolt axles I don't see any problem here, other than the seller not being honest.