I bet this has been asked before but I couldn't find what I wanted on my searches. I have a 2001 CR125, and I last changed my transmission oil May 16th. I don't race and I've probably but maybe 4 hours on it since then. I'm not totally ready for a change, but after the next one or two rides probably. For my first change, I followed the service manual's advice, it said use Honda HP Transmission oil or Honda GN-4 10w-40 and I had a quart of GN-4 from my XR, so I used it. Used 600cc like I should have and all that. Since then the bike has been perfect, as it was before, but I mean to say that there have been no slips or misshifts from using automotive type oil. The service manual also says or an equivalent weight oil, so I'm wondering what to buy for the next one. I'm not sure if I'll be able to make it to the nearest Honda dealer right away, but I can easily make it to another shop to get Bel-Ray or something. But yesterday when I was there, I was only seeing like 80 weight or 90 weight gear oil. I even have a bottle of Tradco or something 90 weight Gear lube, I used that in my Foreman I think and it was good. Basically I want to know what's better, a 10w-40 weight automotive oil or a heavier (I'm assuming 90 weight is heavier but I don't know) transmission oil. The book does not specify to use one of those types of oils. I just want to know the best thing to get to keep the transmission and clutch smooth and and right.