[plain OM]

I can't say with any certainty, but would imagine any from a 2000-4 Outback or Legacy should do if the rest of the original transmission and front differential remain.

However, I might be reluctant to install a used center differential, particularly because the viscous coupling in the differential is probably the first thing to go bad. If the used one comes out of a car with high mileage, or perhaps had a problem which would not be verifiable before installation, you could be back to where you are now (http://www.subaruoutback.org/forums/66-problems-maintenance/38541-viscous-coupling-center-diff.html).

Just to be clear -- do you need to replace the whole extension case and the internals, including the center differential, or or only the center differential? (Seen this thread? http://www.subaruoutback.org/forums/66-problems-maintenance/39181-clunking-noise-when-turning.html)

 

[plain OM]

Everything is busted.

Might I ask: What happened?

http://opposedforces.com/parts/ can be a useful site for researching compatibility. For example, I just did a quick look at Impreza and then Legacy (Outback) MT extension cases, and they're the same part number (32130AA171). Same could be done for the other parts needed. (Impreza and Forester would also be the same.) This could give you both model-to-model (Outback/Legacy/Forester/Impreza) and year-to-year (and even build-date) compatibility comparisons. Here's an example page: http://opposedforces.com/parts/lega...ion/mt_transfer_and_extension/illustration_2/