The manual says Recommended Gear Oil: SAE90. Can I use some left over Red Line 75W90 Gear Oil? It is rated GL-5+. Are there brass parts in a CVT scooter transmission?
I use 75/90 GL5 in my scooter final drive - it's just some spur gears. I guess it picks up about 0.01 hp with the reduced drag...and you can really feel it.
I never found brass parts in my final drive gearbox of my Piaggio scooter, I used Motul Gear 300 75W90, fully synthetic. I figured the less friction losses the better in a 125cc scooter.
I wouldn't consider it a lifetime fill, even tough I know people that changed their gear oil for the first time after 30.000 miles, I changed mine after 1500 miles and then after 1500 miles again, and the gearbox oil was dirty. And were Bitog members after all, there's no lifetime fill for us
I use M1 75W90 Synthetic in all my scoots with ZERO issues. You'll be fine. Even in the two that call for 10w40 motor oil (Honda Elite 250 and Honda Helix)