amazing to me how many people do not read the whole OP.
Minor rust, some 0000 steel wool used dry or dipped in something like Hoppe's as long as its a blue finish. Nickel plating (which he did say it was not) can be damaged by using Hoppe's by the ammonia eating away the underlying bonding plate of the finish.
Keep the steel wool fresh and it will work over time. Use compressed air or a good natural fiber paint brush to remove the debris. If you have some fading on the edges of the gun, a good cold blue from Brownells will work to touch up what you have. then re oil the gun.
Call brownells about the grip screw, they very possibly have one in stock.