If parkerized, take a look at some of the paints available.
I rewelded a sight onto a CETME. Prior to assembly, I touched it up with a little, and it looks like factory.
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Life Member NRA
Life Member NAHC
Former President of the ECPT (Eifel Combat Pistol Team)