I have been using Castrol synthetic 20/50 in my 87 1100 sporty and someone told me I should'nt use that in the harley. They said to use harley oil or even oil that is for diesel engines other than the Castrol. I didn't disagree with him because I never heard that before. Any feedback would be helpful, I hope I haven't been putting in the wrong oil and doing any kind of damage to the bike. Damn.