This is what a lot of guys who collect stuff like this do.
Use regular old WD-40 on the exposed metal. Just use an old towel, not anything especially abrasive. You can put it on and let it soak for a while, then rub vigorously. You should get all the crud but none of the metal or parkerizing off this way. When your done with that put a little light oil on the blade (I like Remington aerosol gun oil, but any light oil will do). Unless the leather is really dry I’d leave it, if it is I’d use a little oil on it (and / or the sheath) too.
This is more a good cleaning than a restoration, which I agree is probably not something you need or want to do.
If you do want to go that route you’d need to strip the handle leather off, remove the finish, do a good sharpening, re-parkerize and then put a new leather wrap on it. You probably want to find a knife-smith to do that for you, if you need to go that route. (Say if the above doesn’t result in satisfactory results, or the blade is deeply pitted or rusted).
You can even find it at WallyWorld now; used to be a pretty specialized gun oil.
“This is what a lot of guys who collect stuff like this do.”
Then they are amateur collectors. WD-40 is a SOLVENT - it is not an oil. WD-40 will RUIN the value of just about anything with a patina.
Just wipe lightly with an oiled cloth.
My father (USMC) was in the Pacific in WW2. He gave me his K Bar and his dog tags. He had scratched Guadalcanal 44 into the leather sheath. Other than cleaning the blade up, I have done nothing to it. Actually in pretty good condition. Of course it was made in America. I don’t know if they are now.
I also have a well used machete stamped “Sheffield Steel” on the blade that we used on our camping trips with him as kids. I don’t believe it is valuable in a monetary sense, but in addition to the personal value, I like the notion of a blade made of British steel, from days when it mattered. A different world to be sure.