Well...I have been trying to figure out what is the best...oil to use in My 2008 FXDC Super Glide. I have been searching for almost a month now and from what I can find....the BEST oil is " What you are confortable with"!!!! In my 6 Yammies I had since 1980 to 2008 I always used Castrol 20w50 Motorcycle oil...and never had any problems. But now with the Harley.... I am going to try AMSOIL..20w50 in the Engine.....10w40 in the Primary....75w90 or 110 Gear lube in the Tranny.....sure hope those guys at AMSOIL know what they are talking about. They tell a good story....so I will see this spring....when I change my oil. I live way up north ...in Northern Canada.....where we get winter 5 months of the year....cuts down on the ammount of miles you put on your bike....or you can ride and freeze your face off. I am wondering if I use synthetic oils.... if it will be better in cooler weather...we get some hot days...but the majority of our weather is cool...and when you get into the mountians...it stays cool. Also storing the bike in a unheated shop...where it can drop to -40... (I do the winter storage thing )...but I wonder if synthetic oil would be better???? more world peace please!