I make some progress, but not sure it's actually good. The surface cleanup a lot better with lead away cloth. I will try to take some pictures tonight as I didn't take a picture after using the lead away cloth.
Just to clarify, the revolver was stored in a locked box (not sealed like pelican case). The locked box is stored in a room with dehumidifier. If the revolver was stored in the safe, I think the problem might not happening as the safe got extra humidity control. I have 4 revolvers save in this locked box. The other 3 revolvers do not have any symptom.