have the same problems here mingin.
problem only really exists with 2nd gear. 1st - 2nd shifts feel very dodgy, sometimes crunching - and this is with very soft slow shifts.
usually when cold, it wont even go into 2nd at all.

i have Motul FF Comp oil in the box which hasn't really helped.
will be trying the RL Lightweight Shockproof next since i have had good experiences with it in my old wrx.

not what you'd expect from a 20,000km old 05 STi.
i have yet to query subaru about the problem... definately feels like a gone synchro.

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Julian
05 STi