I'm sure a cheap option is available but I use a model railway track cleaning rubber for gently working rust off metal fittings on uniforms along with some Tamiya modelers masking tape to protect any areas in case I slip up placed around the area I am working on. 

Here's images of three of my latest leather patch works, 11th Combat Cargo Squadron (Elephant) , 435th Fighter Squadron (Bugs Bunny) and an 832nd Bombardment Squadron , enjoy :) 

MUCH Thanks ocsfollowme, for these images, finally got it nailed down it appears !!!!!!!!!!!!!!!!!!! Johnny  

Great coat and history. Thank you for sharing. 

Thanks. Nah, I won’t replace anything, I also like it as is

Thanks Pete!!   here ya go!

I wouldn't recommend tap water for any fabric cleaning or restoration. Maybe distilled water.   For hardware elements that can rust, wipe them as clean as you can then maybe some kind of varnish to cover them. If they're removable, would nickel plating be acceptable? I've seen it done enough times on restoration videos for toys and such on youtube.

I believe the SAM patch is like the thai made versions listed on page one. Hopefully this shows that this style of patch was indeed made during the war.  

What is printed on top of the spoon?  I believe the spring and hammer is original WWII vintage but would like to see a pic with hammer in the closed position to confirm.  

Amazing find.  I hope you don’t replace the ribbon.  Perfect as-is.