Yeah all the stories out there of what works for other people muddies the water... I don’t think there’s one fluid that works for everyone. All I know is that motul motylgear doesn’t work for me on downshifts.Interesting, but various shifting complaints have been reported resolved by various oil changes from stock, to return to stock, and to "special" mixtures of more than one type/brand. I've personally run Gear 300 for the last 100K or to 240ish with no shifting issues.
Funny thing is my dealer who stands to gain from the higher price motul they carry, still recommends oe tranny oil. I pushed for motul so he said do motylgear since it’s only semi-synth and Gear300 was getting some reports of shifting quirks. Maybe a few years from now when I have a daily that isn’t the STI, I’ll give Gear300 a shot, but for now while it’s my daily and autox car that sees so many kms/miles regularly, I’ll stick oe since it works well for me. Might not be silky smooth, but it never gave me problems either.
People need to find what works for them. I think it comes down to shifting style and possibly model year STI tbh. I’ve read lots of earlier STIs having luck with gear300. Maybe there have been material changes and slight differences in the transmission over the years? Might be “the same” tranny, but who knows if tweaks were done through the generations?