I have a spare rear diff from a my00 Impreza turbo - it did around 70k kms for 4 years before I got bored of trashing 5 speed gearboxes (4 - including one rebuilt with PAR gearset!) and fitted a JDM 6MT which needs a different ratio of CW&P (I used a Forester diff housing/CW&P which I fitted a plated diff into).
It lead a hard life, but is working fine and has relatively low kms - I've actually never heard of them failing before seeing this thread. I'd sell it for €75 if anyone needs one.
Richard
Edited to add: my diff for sale is off a Euro spec car, and is NOT suitable for fitting to a Japanese import. JDM cars used a different ratio to the cars they exported, meaning if the box is JDM, then so must the rear diff be (and visa-versa). Fitting a mismatch will see your centre diff fail, as well as increased fuel consumption, loss of power and unstable handling.