Trapdoor Rifles

Hey Guys,
I have a 1873 Trapdoor Carbine which has a "C" stamped Buffington rear sight assembly. The carbine serial number is in the 112XXX range so I believe it was made in 1888. My problem is that I cannot adjust the elevation ladder on the sight. Windage works fine. I've removed the sight from the rifle and have been soaking it in PB Blaster for over two weeks now and the adjustment knob will not budge. Since I don't know how the ladder is adjusted I'm hesitant to force anything. Is there some type of worm gear that adjusts the ladder or does the ladder slide up or down manually once the knob is loosened? Any input would be appreciated! Thanks.
Bruce

112,000 would be 1879. The Buffington sight would have been an upgrade. The slide is moved manually once the knob is loose. The army DID pin a great many sights to prevent windage adjustment, but the elevation should work. Try a bit of heat and/or GENTLE tapping, or another solvent. It SHOULD eventually come free. There was an experimental version of that sight with a rack and pinion elevation, but was never used on carbines.

Thank you for the response Dick...and thanks for the clarification on the build date! I'll try some Kroil to see if that does any better. If not, I'll apply a little heat.

Dick
Kroil did the trick. Got it loose and now functions well. Much obliged!
I you wouldn't mind one more question, I wonder if you know what the front sight blade height and thickness was on these 1873 trapdoors with Buffington rear sight? The replacements I've seen offered online vary from a thin, tall blade to a shorter, thicker wedge. I've only had mine out one time at the range when a buddy loaded up some light loads with 350 grn bullets and it was shooting about a foot high at 50 yards. The front sight blade on this rifle was obviously replaced at one time with this piece of white plastic. Any help would be appreciated!