98 Mazda Protege 1.5L Tappet Shims

Engine runs fine with no smoke. But have click or clack noise. Engine has DOHC with tappets and shims for adjustment of valve lash. Stethoscope says loudest noise is from #3 cyl intake valves. Specs are .010" - .012" tapet shim to cam clearance. Most run from .016" - .018" but exhaust side of #3 has .022 clearance. I think I will replace all four shims for only #3 even though others are also out of tolerance by .004" to .006". Cams are ok.

How do you determine what size shim to get in a Mazda. Is there some kind of code that tells the installed shim's thickness?

Also, this is a "For Resale" car. What do you think of wisdom of only replacing #3 shims. Engine is quiet and has 100K.
Thanks,