[Dean]

Not trying to start a battle or nit pick, but while they may sit in the same location in a drive train, a transfer case is significantly different than a center Diff. A TC splits power front and rear evenly at one or more gear ratios. A center diff is just that a differential of some form with fixed or variable torque split usually at a single gear ratio.

I do not claim to know anything about Evo transmissions, but it is unlikely that the gearset and synchros are the same on the two gearboxes.

Those are the weak point of the Subaru trannys and many of us make a conscious choice to use the LW shockproof even though it is a GL-4 fluid to protect the transmission and make shifting significantly smoother, especially 1st gear downshifts. This may cause additional wear on the diff, but to the best of my knowledge, I have never seen even anecdotal evidence of that wear or failure prior to tranny failure.

Shared fluid forces compromises, and especially on the 5MT, I would use whatever will protect the transmission at all costs.