I once talked to a dealer mechanic and asked him why I couldn't just put my KLR valve shims on a surface grinder to bring them in to spec. He told me that they always take thicker shims when they go out of spec.
I never went back to that shop. I suspect that he has never really adjusted any valves as a part of routine maintenance.
Every bike I ever owned, was the best bike I ever owned when I owned it. Well, except for that one Harley