RGC, Your barrel is original, see if you can get the front sight off. Some come right off. Your problem will be solved.
Look carefully at the sight. Is it issue or a Lyman target sight.
If it is issue, knock out the cross pin on the top side of the barrel.
The small pin holds the sight blade. Leave it in.
After the pin is removed. Use a 2x4 . Place it on the top back of the sight.
Tap the block against the sight to move it forward, it it moves any. Clean and grease any part of the barrel forward of the sight.
Keep taping it forward till free.
Now clean and oil the Key and front slot. It might fall out.
Check for rust or other stuff.
Some times the Dragon Wins and I bet you get Lucky and it falls off and is pristine A4 under the removed sight....