My local dealer ran out of the regular Amsoil 10w40 and substituted with Amsoil 10w40 motorcycle oil. Low and behold the lifter noise problem I had with my '96 Miata, at start up and after hot laps, went away with the motorcycle oil, haven't hoid from it since. Are there any disadvantages to this vrs. using the standard Amsoil 10w40? Can someone tell me what are the additional additives are and their function? I did read through the Motorcycle oil forum but could not find a direct answer.