When I switched from 10-50 to 10-40 (per the owner's manual), the clunk went away. Perfect shifts ever since then. I have always used Amsoil fully synthetic. The only difference was the oil weight, and evidently that was the problem. I believe the original Triumph shop manual said 10-50 but the owner's manual said 10-40. Anyway, the 10-40 works right for my bike.
