I picked up two 40x light-powered magnifying pieces - for $7 shipped on eBay. Opens up another world of fun with these oldies. One example was it saved me from ruining the tiny threaded rear sight screw on my Sharps, as the end of the thread had damage I couldn't see with my 4x. I aligned the thread for easy screw-in. Lots of worn/hidden roll-pressed markings became clear.
Does the rear sight have any model-matching markings, maybe on the underside? Condition match with the sight vs. the barrel and lockplate? Could it just be the metal for this and other rifle/carbine sights are just not heat treated and protected like the other parts (Damascus steel barrel?), and will simply be more susceptible to the elements?