Shim and bucket valvetrain systems are extremely stable. The bucket is guided by the head which reduces side load on the valve guide, and the cam wiping surface area is wide, which reduces cam and tappet wear. I don't think there is any way for the lash clearance to increase from wear under normal conditions, however there is always the possibility of some wear in the cam journal bearings. Variation in measured lash more likely relates to how the cam is positioned in the head, and/or how much oil is retained in the journal bearings. As mentioned earlier in the thread, if you use the 180* cam positioning method before checking lash the adjacent valve will be pushing up on the cam and skewing it in the journal clearance. This results in the clearance being greater than would be the case if you check the clearance using the factory kawasaki specified cam positions (which put two adjacent valves on the base circle). If someone was using the factory cam positioning method and measured more clearance than the last time they checked the valves than I'd blame the way the cam is positioned, and the amount of oil in the bearing journals in some way. I doubt the variation in clearance would be more than a thousands or so anyway, and measuring such a small clearance is always fraught with the possibility of measurement error entering the system.
