BRZ transmission oil question

[MoonieGT]

The BRZ/FRS twins have notoriously notchy gearboxes; however, a simple transmission oil change from the factory oil to Motul is widely reported as making a remarkable improvement in shift feel. I did the swap in my BRZ and the first and second times I drove the car, the improvement was magical. It was such a slick gearbox! But from the third time or so after I took the car for a drive, the gearbox went back to feeling kind of notchy again (perhaps not as bad as the the factory oil, but a far cry from the magical heavenly feel that it had the first time I took it out after swapping to Motul). Any thoughts as to why the heavenly feeling went away? I've ordered some more Motul, and I'm going to drain and refill this weekend to see if that helps.

My thoughts: 1) some of old fluid remained in the transmission and contaminated the Motul? 2) the car wasn't level and the fluid level is a bit low?

I'd really like to get that heavenly feeling shifter back...

[OZMDD]

I suspect #1 is the best explanation, though I am not familiar with that gearbox. My next thought would be to find out if the gearbox contains yellow metals, if the factory spec fluid has special friction modifiers, and if the Motul is a GL-4, GL-5, or something else. With the NC gearbox, GL-4 was the key to keeping the synchros and yellow metals happy.

[POS Racing]

Yea what OZZMD said!

What does Toybaru recommend for fluid?? Do they Specify GL4??

We have learned with the Miatas a GL5 fluid can make for some notchy shifting. But you'll still have douche canoes on the interwebz touting the wrong stuff.

[POS Racing]

Toybaru has this to say on the fluid - https://www.joomag.com/magazine/suba...10946?page=421