I'm just going by what my 06 Ultra Classic owners manual and shop manual say. I double checked and both recommend Formula+Primary and Trans lube in the Primary and Transmission. I ran the Synth3 in every thing in my 05 Classic and traded it in with nearly 30K miles on the clock. No problems at all. When I traded for the 06, I asked two different Harley mechanics that I know at two different dealers. Both said the same thing, the Synth3 is fine for the motor and primary and probably OK for the tranny, but people that plan to keep their bikes a long time would be better off with a heavier trans lube. One of these guys used HD dino oil, and the old gear lube and primary lube, the other used Synth3 in the motor and the new Formula+ in his primary and transmission. I'm not saying that the Synth3 isn't OK for everything, HD can't very well deny warranty or anything like that since they recommend it, but my owners manual tells me different.