subaru stuff has detergents in it. i've always been told to avoid that stuff. whatever you get make sure it has a friction-additive, some idiot put "normal" stuff in my 5mt and every gear ground like hell because the syncros wouldnt catch, untill they put Pensoil Syncro-mesh stuff in it.
by the way... GC8 STI v5? i'm a bit curious about your car.