FL needs to be used as a lube and protectant to a clean gun to begin with. The best example I can use is my BCG in my AR . I followed directions and cleaned , heated and treated My Bolt with the FL. After many days at the range I went to clean it and the carbon just wiped off with a clean cloth.
They use to advertise that it removes rust and corrosion. I did a home exp. on this and found it does not remove corrosion. I have a 1976 Win model 94 that I bought as a truck gun. It was neglected and has a more than normal coat of surface rust on it. I used the FL to treat it after cleaning it the best I could and have not noticed any futher corrosion taking place.
Now.. On to my Glocks. I treated them per instructions , and use only the FL to clean them and it works perfectly. I have treated a Browning Hp and My Hk P7 the same way. Once done shooting , they clean up like a dream using FL as a cleaner. I really think that getting the old oils off and "Treating" the gun with the FL solution is the key. I ankle carry a 26 everyday. After a few weeks of lint and wearing it . I still feel the smooth teflon like surface the FL leaves behind. I blow it off with an airhose and Check function and it is like new.