i just switch to M1 in both holes, seems to be fine, i guess there is more of a chance of clutch slipping with syn in the primary. once i switch to a energy one clutch, i may switch to belray sport transmission for sportsters. i may just contiue with M1 syn or just go with dino 20w50 or just the formula + or even M1 gear oli but i hear that its both bad and good. I want to use something that is easily available in my area.

 

I have been using Red Line 75W90 GL5 gear oil in my sporty trans for some time now with great results. Much better shifting and more positive clutch hook up. I plan to continue using the gear oil for the superior results I'm getting.

 

Mobil 1 75W-90 gear oil works great as well. Bel Ray is always a good choice too.

It seems to work fine in my bike, a 1991.

John