I just dropped my ’05 Classic off at a guys shop for a 10K inspection. He has been running a cycle shop on his own for years. We got to talking about lubricants, since I have already serviced them myself. He said that the HD Syn3 in my engine was fine, and the M1 75-90 in the Trans was OK. Then he went on to say that the only engine oil he has seen problems with was Amsoil. In less than a year he has rebuilt three engines with flats on the crank shafts. All used Amsoil 20-50 100%. I did not ask about the details of each bike. With all the other highly rated products out there, this would be enough for me to switch.