has anyone with an STI 6 speed had hard notchy gear changes in a box that they personally know hasn't been slaughtered?

originally my gearbox was near impossible to change down to 2nd or 1st when it was cold

example:: start car, back out, drive a cuppla hundred metres, roundabout, need to come to a complete stop to get from 3rd down to 2nd or 2nd down to 1st. i took this to subaru, complained (while i had a cuppla months warranty left) and they put auto trans fluid in to thin it up. problem solvered.

well, now 4th is a beeyatch! it's notchy going from 3rd to 4th and it's NASTY from 5th to 4th. this gearbox has not been slaughtered since i've owned it, if anything, only the clutch because i'd rather slip it than do a box, the gears have never been smashed. i wouldn't be surprised if the 4th problem is synchro's thanks to the auto trans fluid...

so.... 1. has anyone had the same problem?
2. has anyone solved this problem with a specific oil?

i know, i know, redline lightweight shockproof is the go... i know how good this oil is, i've had it in the past.. but i want to know from someone who has used a specific oil and proven it's worth.. and i'll change it tomorrow.

otherwise, i keep going till my synchro's are gone and i'll put all new synchro's through the box. (and whatever else it's worn)