I have a 2005 S83 boulevard with about 18000 miles on her. About 200 miles back I developed a tapping nose in the rear head. It sounds like a valve needs to be adjusted; my shop told me the 05 have hydrolith lifters, if so the only thing I can think of is the thrust washer is shot. Ps they told me to keep an eye on it if it gets worse to bring it in, no sh-- . Am I looking in the right spot? And how much damage will that do if I let it go for a wile