I just got a rear diff for $336 shipped. There are some out there for around $420 shipped.
I had a buddy rebuild the 5mt new synchro's and a 3rd/4th gear.
I have a Spec 2+ clutch and their LWFW in the car since about 72,000 miles.
You can use a WRX single mass FW, that is what most people do.
Here check out my thread for some info you may be able to use.
203,000miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.
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