I just bought a 85 kawasaki gpz550 to resell in the spring and hopefully make a small profit. The previous owner stated he used castrol gtx 10w40 in it. I bought some yamalube 20w40 (odd weight) because it was priced right for the oil change. I am very impressed, the tranny on this bike shifts very well compared to the castrol that was in it and in fact, i think this may be the best oil i have used as far as tranny feel goes.