I've got a Viscous unit, but I don't know if it'll mate up with your axles. This is the actual part that bolts to the ring gear, not a complete diff...
Brian, The WRX is a R160 rear end just like the RS and L. I think it will fit just fine. My L axles fit into the '00 RS diff carrier! So far my L axles fit the older Legacy diffs and the '00 viscous.
The only difference is the splines on the axle, that's why I don't know if it will work. I've got the matching axles for it, but they're for a GD sedan and they'd be too long for his GC. I suppose we could always see if one of his axles will fit...
hehhe I think he should just get an OLDER 4.111 from the Impreza at the U PULL yard and stick in the phantomgrip, which should work WAY BETTER than the viscous unit.
eh...other suby owners got dibs on it. I'll just keep looking. Cusco LSD is too much too, Fuji could you buy it for me as a christmas present?