nice rifle, great pics,
front sight, bayonet lug, and cocking rod are replacements.
likely field repair, not a rebuild. rifle has seen some sevice for sure.
cleaning with solvent will show that the brown is likely rust. of if your lucky, dried grease..hopefuly the later.
your pics show what iv been saying for years,
the correct color for Remington A3,s is light grey..under the wood line clearly shows this...
isnt green, brown, black ect, its light grey..thanks for sharing.